Grand Canyon 3-D Tour
North-Northeast of Pearce Ferry
A chronology of transitions from:
Near River Mile 280
Pearce Ferry Rapid
1) Lake Mead
2) To a new superimposed path for the Colorado River
3) Which became a “riffle” near the old Pearce Ferry
4) This “riffle” became a moderately severe rapid in late 2007.
The combination of silt deposited by the river along with highly
variable water levels in Lake Mead will continue to produce rapid
changes in years to come.
views 1985, 2010, and 2014
The photographs shown above and below were posted on NASA’s Earth
Observatory page on Sept. 22, 2010. http://earthobservatory.nasa.gov/IOTD/view.php?id=45945
Both photographs show:
1) The extreme western end of the Grand Canyon (lower right edge)
2) Pearce Bay (To the right and slightly below the center of the photos)
3) Wheeler Ridge (Above and to the right of the center of the photos)
4) Iceberg Canyon (Upper left quadrant)
5) Gregg Basin and Sandy Point (Lower left quadrant)
However, the top photo was taken Aug. 22, 1985 while the bottom photo
was taken Aug. 11, 2010.
In the 25 year interval from 1985 to 2010, the Colorado River deposited
many hundreds of millions of tons of silt into the former upper end of
Lake Mead. Water levels in Lake Mead have been dropping since 1998. The
narration below describes the result.
The picture above is via NASA’s Earth Observatory
shows the status of the lower end of the river as of July 21, 2014.
Lake Mead is currently at its lowest level since it was being filled in
the 1930s. The Colorado River’s delta has now reached the north shore
of Sandy Point.
Construction of Hoover Dam (Boulder Dam) began in
and was completed in 1935 as part of a project to “reclaim the
desert for productive human usage”. (Hence the name “Bureau
of Reclamation”.) By early 1941, the Colorado River had filled
reservoir to capacity to form Lake Mead.
The historic photograph below was taken July 12,
shows what the upper end of Lake Mead looked like before large amounts
of sediment had accumulated. (Estimated water level is 1176 feet.) This
and other historic photographs of the area can be found at the USGS
Earth Explorer web site at http://earthexplorer.usgs.gov/
(For the photo below, use the map to zoom in (and click ) on what used
to be the east end of Lake Mead, pick a date prior to 1955, click on
“Data Sets”, expand “Aerial Imagery”, check “Aerial Photos
Frames”, and click on “Results”.)
The silt-laden Colorado River exits from the Grand Canyon
(lower right quadrant) into Lake Mead. Pearce Bay is in the lower left
portion of the lake, and what will become the location for
Superimposition Rapid is just to the right of the two points of land
that stick out into the lake just to the north of Pearce Bay. If you
look just to the right of the northernmost of the two points, you can
see a small island. There is a submerged ridge that connects this
island with the higher ground to the left, and after another 50+ years
changes to Lake Mead, the river will hang up on this old ridge to
produce Superimposition Rapid.
Before Glen Canyon Dam was built, the silt load of
Colorado River (as measured near Phantom Ranch in the Grand Canyon)
averaged 3 to 5 tons per second. (Different sources give different
amounts) Before Hoover Dam was built, this
sediment ended up in the Colorado River’s delta, but after it was
built, it was all deposited in Lake Mead.
The topographic map above from http://www.topozone.com
old ridge that the river is now crossing. (The old ridge is the narrow
peninsula that sticks out into the lake just below the BM 1250 label.)
The lowest lake shoreline shows that the top of the old ridge was
exposed above the 1157-foot level. (The estimate date for the low-lake
contours is about mid 1972.) Also the 1160-foot contour line is shown
on the ridge which increases the pre-erosion level of the old ridge to
above the 1160-foot level.
The small island that could be seen in the
photo shows up as the small hill (closed 1200-foot contour) at the end
of the peninsula. The Pearce Ferry take-out is off the bottom edge of
the map to the left of center.
An April 15, 1962 photograph at http://www6.nau.edu/library/scadb/imagedisplay.cfm?item_num=9383&type=Image
also shows this old ridge exposed above an estimated Lake Mead water
level of 1157 feet. (View looks south with the peninsula just above the
The picture above shows the location for the
rapid as it appeared in September 1992. (Estimated Lake Mead elevation
is 1174 feet.) The upper end of Lake Mead has filled with silt. Pearce
Bay is in the lower left hand corner. The two points of land in the
upper left corner are the same as shown in the earlier pictures. What
was an island in the first picture and the end of the peninsula in the
topo map, is now the small triangular light area just to the right of
the river. This area will be submerged again during the high water
levels seen in the late 1990s (see graph below), but the final path of
the river will be near what can be seen in this photograph.
Vertical view of what used to be the northeast end
Mead. (Estimated date for the photograph is April 8, 2004. Estimated
Lake Mead elevation is 1140 feet.) The
(historic) take-out at Pearce Ferry (at the lower end of
Pearce Wash) is in the lower left quadrant - near River Mile 280 in the
standard Grand Canyon river guide books. “Superimposition
Rapid” has subsequently formed where the two ridges closely
approach the river - midway between the pin and the left edge. The pin
marks the estimated location of the 1923 photograph shown at the bottom
of this page.
Before Hoover (Boulder) Dam was built, the
exited from the Grand Canyon (off the right edge of the picture) and
flowed left and up across what are now the mudflats in the picture, to
exit off the top edge (left of center). After Hoover Dam was completed,
the reservoir backed up to cover the dark brown area in the picture
with water. What was part of Lake Mead as seen in the first photograph
has now been transformed into the dark brown mud flats.
Over a period of several decades, silt brought
down by the
Colorado River filled in the old river channel and spread out to cover
an area more than a mile wide to form a broad silt flat. The bottom of
the old river channel is some 300 feet down under the silt. (A graph at
shows the river elevations for both before and after Hoover (Boulder)
The graph above shows the water level in Lake Mead
starting with 1980. The plotted levels into 2017 are forecasts via
the U. S. Bureau of Reclamation as of the Sept., 2015 USBR report http://www.usbr.gov/lc/riverops.html
levels can be seen at
The water level in Lake Mead reached its maximum
in 1983. When the lake level subsequently receded from this maximum
elevation, the river had no guide as to the location of the old
channel, and established a new path across the silt flats,
approximately in its current position. Most of this new path area was
periodically exposed and resubmerged over the next 20 years, but the
drought that has set in during the early 2000s has severely lowered
Lake Mead. As the water level lowered, the river became entrenched in
its new path.
Please see “Transition to a more arid
Southwest” (and related technical paper links) at http://www.ldeo.columbia.edu/res/div/ocp/drought/science.shtml
for the reasons why drought conditions are developing. (And be sure to
give the authors an A+ for recognizing the current problem in advance.)
The geological sequence of burying an old
silt/sediment and then establishing a new river drainage system across
the top of these sediments is a process called superimposition. In a
normal geologic time frame, this requires many millions of years. Here,
at the upper end of Lake Mead, a man-made version of the process has
taken only a few decades.
In a normal geologic sequence, a new superimposed
system might end up over the top of an ancient mountain range. If
subsequent erosion removes the softer sediments, it’s quite
possible the superimposed river might remain stuck in its path and
erode its way down through the old mountain range to form a canyon.
Here, in the remnant of the upper end of Lake
silt deposits buried an old ridge. When the Colorado River established
its new course after the 1983 maximum elevation of Lake Mead, the river
happened to end up over the top of an old ridge. When the water level
in Lake Mead subsequently dropped, sediments on the downstream side of
the ridge eroded away. However, the ridge resisted erosion. The river
thus formed a rapid where it dropped from the relatively higher
elevation of the ridge to the relatively lower elevation downstream. It
seems appropriate to name the rapid “Superimposition Rapid”.
(Alternately, if the rapid were named for its geographical location, it
might be named Pearce Ferry Rapid or Pierce Ferry Rapid.)
The picture above shows what the landscape at
“Superimposition Rapid” looked like before Lake Mead dropped low enough
for the rapid to form. The Colorado River is entrenched in a path that
forces it to cross an old ridge. The area
where the river crosses the ridge can also be seen in the first Google
Earth picture - midway between the pin and the left edge. In both views
enters from the right and then flows toward the top of the picture.
The Google Earth satellite picture (above) was probably taken on April
8, 2004 and covers approximately the same area as the Vishnu Temple
Press photo below. With a little work you can find the exact spot where
the Vishnu picture was taken. The white sand in the foreground of the
Vishnu picture will match the lower right end of the white sand patches
in the Google Earth picture. (On the left side of the river, above and
slightly to the right of the center copyright labels.)
The photograph above is similar to the Google
picture and was taken on March 22, 2003. It was originally posted on
the Vishnu Temple Press website (Good source for rafting guide books.),
and while it is no longer posted there, you can see the original web
page at: http://web.archive.org/web/20031208154023/www.vishnutemplepress.com/pearceferry.html
The photograph above was taken by Tom Martin at nearly the same
location as the Vishnu Temple Press photograph - but in Feb. 2008. It
is inserted here (a jump in the time sequence) to show what has
happened in the 5 year period from 2003 to 2008. Notice how the river
has dug down through the sediments. (For example, the ridge a couple of
hundred yards downstream in the upper left is now part of the skyline
as the photographic location is now 20 to 30 feet lower.)
As the elevation of Lake Mead dropped due to the
the Colorado River had an easy chance to erode the silt deposits that
were deposited before the drought lowered the water level. The
exception is the ridge. When Lake Mead dropped below the 1120-foot
level in 2007, the river could erode the silt sediments downstream from
the ridge, but the ridge acted as a dam and protected the sediments
above the ridge. The ridge itself became the crest of the new rapid.
(This is the upstream portion of the rapid which is a couple of hundred
feet upstream from the large rock that subsequently emerged.)
The two pictures below are from an aerial U.S.
Reclamation photograph that can be seen at http://www.usbr.gov/lc/region/g5000/photolab/gallery_detail.cfm?PICIDTYPE=13209
This first picture looks east across the
easternmost end of Lake Mead. In the distance, the Colorado River exits
from the Grand Canyon, flows westward (toward the foreground) across
the silt flats, and then turns north to flow off the left edge of the
picture. The old Pearce Ferry takeout is well off the lower right edge
while the location for the new rapid is in the lower left corner.
The picture above is an enlargement of the lower
corner of the previous picture. Both views show what the incipient
rapid looked like on Feb. 2, 2006 - Lake Mead elevation about 1140 feet.
Standing waves from a submerged pour-over rock
ridge) can be seen.
As of late July 2007, the surface elevation of
Mead had dropped about 29 feet from where it was in Feb 2006. The soft
sediments that were deposited by the river over the last 6 decades can
be easily eroded. This leaves two major possibilities. 1) If the rock
in the old ridge can resist further erosion, then a severe rapid will
form on the downstream (left) side of the old ridge. 2) The river just
might be able to erode down through the old ridge. If it can erode
downward, there will still be a rapid, but the drop-off will be less,
and hence the rapid will be less severe.
photograph at the right was taken by
“bobkerry44” on Oct. 7, 2006 and is a copy of the original
which is posted in the photos section at the gcpba Yahoo Group. The
photograph was taken from near the right bank of the river and looks
northwestward across the river to the same portion of the ridge
that appears on the left side in the Vishnu picture.
The Vishnu picture was taken in March 2003 with the water level in Lake
Mead at about 1154 feet. By Oct 7, 2006 the lake had dropped to about
1126 feet. The river had already taken advantage of this height
difference to erode downward toward the old ridge. The pour-over rock
that is in the center of the photograph is part of the top of the old
ridge. As the lake continues to drop in the future, the river will
become increasingly hung up on the old ridge and the rapid will
gradually become more severe.
The following 3 pictures were taken from “North
Point” (the left ridge in the Vishnu picture) and look southeast to
south over the rapid. The sequence is a record of what was happening in
the fall and winter of 2007/2008.
first picture was taken on Sept. 1, 2007 by Duwain Whitis (“Guide to
the Colorado River in the Grand Canyon” by Tom Martin and Duwain Whitis)
This next photograph was taken on Oct. 8, 2007 by
Martin (River Runners For Wilderness) and coauthor of the above river
Finally, the third picture (below) was by Tom
Martin in Feb. 2008.
Two items of interest are of note. The most obvious is the large rock
in the middle of the river. Also there is a smaller riffle about 200
feet upstream from the rock.
Update as of June 30, 2009
The photograph above was taken by David Witton and shows the status of
the rapid as of June 1, 2009. The photo was taken from the left (west)
bank of the river and looks slightly west of due north. The tilted
strata in Wheeler Ridge can be seen in the distance.
The top of the ridge on the left side of the photo was the viewpoint
for the previous pictures. This view looks downstream over the rapid.
The lower part of the ridge reveals horizontal layers of loosely
consolidated silt and gravel that were deposited some 5 to 15 million
years ago. These rock layers are not cemented together as solidly as
the much older rocks that are exposed in the Grand Canyon. Thus the
river has been able to erode down through them fairly rapidly.
As the river erodes down through these more easily eroded layers, the
original submerged rock (which apparently is a patch of conglomerate)
has gone through the following stages.
1) The rock was initially submerged and just produced waves in the
The river began to carve out channels around the rock (mostly to the
left/west). As the river carved the lower channels the rock emerged
above the surface.
3) Further down-cutting by the river has allowed
a ledge to be exposed to the left (west) of the rock. There is also
another submerged rock that shows up near the left edge of the photo.
Update as of
March 5, 2010
The picture above was taken by Tom Martin about March 2, 2010, and can
be seen in the Gallery of pictures at the River Runners for Wilderness
The view is taken from “North Point” bluff, and looks southeast across
the rapid. The river continues to cut down several feet per year
through poorly consolidated, 5 to 15 million year old rock. In the
process, patches of somewhat harder conglomerate rock are becoming more
exposed as the river erodes a deeper channel around them.
A ledge extending westward (from left to right in the photo) from the
original submerged rock is now fully exposed. The river flow indicates
that a further extension of this ledge is just under the surface. The
river forms foaming holes after it pours over the ledge.
There appear to be other submerged ledges just underwater extending out
from the base of the bluff in the foreground.
ledges may make things difficult for rafters in the not too distant
future. Where the river pours over a ledge, it will form a “hole” with
a strong breaking wave on the downstream side of the hole. This type of
water flow can easily flip a raft.
river may end up taking a very sharp, turbulent right turn (as you look
downstream) in between these ledges.
Update as of Sept. 22, 2010
The two photographs below were taken on Sept. 17, 2010. If
click on either photograph you can see a large version of each.
photograph above looks southeast from “North Ridge” and shows the east
side of the rapid – right side as you are looking downstream.
photograph above looks south-southeast from “North Ridge” and shows the
west side of the rapid – left side as you are looking downstream.
What was originally just a rock in the middle of the river is gradually
revealing itself as a ledge that extends across the entire river. As
the river erodes downward, the exposed portion of the ledge is steadily
extending westward. (Toward the left side of the river as you are
If you click on either
photograph, you will get a large version that shows more detail. The
rock ledge has interleaved layers of silt and conglomerate cobbles that
were deposited some 10 to 15 million years ago. Rocks and cobbles in
conglomerate layers were washed in by local flash floods. Silt layers
(without imbedded rocks) were deposited by mud settling out of a
The layers that can be seen in the
ledge were subsequently buried by another ~1,800 feet of
sediments in what was a closed basin up until about 5.4
ago. (The old level top of these sediments is still present at the dirt
airstrip about 4 miles southwest of the rapid – see bottom edge of the
NASA photos at top of page.) Finally, the Colorado
River relocated to its present course about 5.4 million years ago, and
has been busy excavating the whole works (including cutting the Grand
Update as of April 24, 2011
The two photos below were taken on April 23, 2011 by Steve Roberts.
The picture above looks upstream to include the east side of the rapid.
The channel on the east side of the rapid was navigable a couple of
years ago, but it’s now just a small waterfall that bounces off a
couple of ledges.
The picture above shows the main part of the rapid - which flows to the
west side of the large rock. This portion of the river has also eroded
down to a series of ledges. There doesn’t appear to be any navigable
route other than bouncing off a ledge or two followed by a plunge into
the deepening “hole”.
If we look still further out
into the future over the next couple of decades, Superimposition Rapid
will just be a temporary phenomenon. Even with Glen Canyon Dam blocking
the silt flow that used to come down the Colorado River, there is still
an inflow of silt from the Paria, the Little Colorado, and smaller
tributaries. This silt will continue to accumulate in what used to be
the upper end of Lake Mead. The exact details of where and when this
new silt will settle out will vary with the water level in Lake Mead,
but the new silt will eventually bury everything that is visible today.
This will include Superimposition Rapid, which will eventually be
buried - never to reappear again.
The photo above was taken by Andy Pernick of the
U. S. Bureau of Reclamation on April 25, 1997.
The view looks NNE up Iceberg Canyon when Lake Mead was nearly full
(water level 1200 feet), and before silt filled Iceberg Canyon. The
site of the uppermost Iceberg Reef Rapid/Iceberg Rapid (Devils Cove
Rapid - the “Wave” of 2008) is about “one island length” to the right
of the elongated island that can be seen near the left edge of the
photo. What appears as an island in this photo is the white colored
point to the left of the incipient Devils Cove Rapid in the next photo.
The sediment that is brought down by the Colorado River continues to
build a delta out into Lake Mead. This sediment has buried the old
river channel under some 300 feet of mud/silt. As the water level in
Lake Mead drops lower, the river establishes new channels across these
silt flats. Since the river has no guidance as to the location of the
old channel, the new channels meander randomly across the silt flats -
and in the process these new channels occasionally end up relocating
over the top of old buried ridges. Then, as the water level in Lake
Mead drops, the river hangs up on the hard rock of the old ridges and
“pour-over” rapids develop on the downstream side.
The original copy of the above photo was taken by Andy Pernick of the
U. S. Bureau of Reclamation on Jan. 8, 2009. The original picture
(which includes better detail) can be downloaded from:
The view looks toward the NNE up Iceberg Canyon. The original river
channel hugged the cliffs on the right (east) side of Iceberg Canyon.
However, the river has formed a new course as indicated by the blue
dots. Areas where the new course of the river crosses over buried
ridges are indicated by paired dots. The dots represent the estimated
path of the river as of July 1, 2009. (Also see topo maps and photo
below.) The river’s course is subject to change with no advance notice
- which should be borne in mind by anyone running the river.
These two topo maps (above and below) show the same area as the aerial
photograph except the estimated course of the river is shown by red
dots. (Red dots show up better than blue dots.)
The most northerly of the paired dots is Devils Cove Rapid - otherwise
known as “The 2008 Wave” which surfaced during the summer of 2008. At
that time, the upper end of Lake Mead was just a short distance to the
southeast. During the winter of 2008/2009 the water level in Lake Mead
rose several feet and submerged the wave - as shown in the Jan. 8, 2009
By the time the lake level dropped again in 2009, additional layers of
silt had been deposited. The delta now extended an additional mile
beyond the 2008 position and the river developed still another new
A second rapid (Burro Spring Rapid) formed
about 0.6 miles SSW of Devils Cove Rapid where the new course of the
river crossed another old buried ridge. This location is shown by the
second set of double dots in the above photo and topo maps. The
possibility exists that a third rapid may develop still further
downstream where the river makes a close approach to another ridge in
the lower left corner of the above photo.
The photo to the right was taken by Tom Martin
about July 1, 2009.
Tom took additional photos of the rapids in this area, and these can be
seen at: http://www.rrfw.org/gallery/index.php
The view looks SSW over the new rapids with the south end of
Iceberg Canyon in the extreme lower right corner. The persistently
shrinking Lake Mead can be seen in the upper left quadrant with Sandy
Point sticking out into the lake from the left (east) shore line.
The uppermost of the two new rapids (Devils Cove Rapid) is in the lower
right portion of the photo just above the green vegetation patches that
bracket the river, and just below the large sandy area to the left of
the river. In between these two locations, the river crosses a
sediment-buried ridge that is part of Iceberg Reef.
This rapid emerged briefly in the summer of 2008 and for a while formed
“The Wave”. The ridge that the river crosses shows up as the small
elongated island that was visible in the 1997 photograph.
In the Jan. 2009 photograph, there was a large muddy area where the
river was building its delta out into the lake. By July 1, 2009 the
lake level had dropped some 15 feet. The mud was exposed and
subsequently dried out to form the whitish sandy area in the July 1
Meanwhile, the river extended its path
further out into the lake, and in the process, crossed another buried
ridge. As the lake level dropped, the river eroded down thru the silt
and sediment until it hung up on the top of the old ridge. A new rapid,
Burro Spring Rapid is the result. Its location can be seen in the photo
where the river turns to the right and exits the sandy area. ( A
close-up of Burro Spring Rapid can be seen at: http://www.rrfw.org/gallery/index.php
May 20, 2011 Update
The runoff from the above average winter snowpack in the Rockies will
submerge everything from Iceberg Canyon on down. The “Wave” that
existed downstream from Iceberg Canyon will be submerged by the end of
Aug. 2011, and it will subsequently be buried by silt. It will never be
The backup from the rising water level
in Lake Mead may extend all the way back up to Pearce
Ferry/Superimposition Rapid. As the river gradient from the rapid to
Iceberg Canyon decreases, the river will start filling its channel with
new silt. This will decrease the drop across the rapid with the result
that it may moderate its intensity somewhat during 2012. (Details
subject to future Lake Mead water levels.)
July 12, 2011 Update
It looks like the runoff from the heavy 2010/2011 snowpack will be
enough to submerge everything below Pearce Ferry/Superimposition Rapid,
and the rapid itself will be buried under the silt backup system. The
rapid should rapidly weaken starting in Aug. or Sept. 2011, and
disappear entirely no later than the end of Dec. 2011. It will probably
never exist again in the future. In the future, Lake Mead’s water level
may again drop to low levels, but by then the silt inflow at its upper
end will have permanently buried the rapid.
Ferry/Superimposition Rapid will exist only as footnotes to history –
and in the memory of river runners who ran the rapid, the “Wave”, and
everything in between. This web page will continue to exist for a few
years to record what happened; but inevitably at some future date, it
will also disappear into the forgotten haze of history.
– Jan. 11, 2012
The photo above was taken on Jan. 3, 2012 by Brady
Black and posted in the Mountain Buzz forum at http://www.mountainbuzz.com/forums/f11/pearce-ferry-rapid-35506-7.html
There was still a noticeable current at the rapid, but this was due to
the channel constriction between the rock and “North Point” as opposed
to any elevation drop of significance at the rapid.
Despite the current low snowpack levels in the
Lake Mead is expected to rise a little higher yet than what prevailed
at the beginning of 2012. This plus the unrelenting silt accumulation
should mark the end of the rapid.
R.I.P. oh mighty rapid.
The continued long term drought in the southwest
caused Lake Mead to drop to its lowest levels since it was being filled
in the 1930s. The rapid at Peace Ferry is fully exposed and is quite
severe again. A new rapid may develop a short distance upstream from
the former Driftwood Island ( See http://www.durangobill.com/GCTourLowerSuperimposition.html
“The Wave” rapid just below Iceberg Canyon should be fully
exposed and may become severe by late summer 2015. (And may be
unrunnable in 2016.) It looks like river current exists until you pass
Sandy Point. South Cove may become unreachable by boat in 2016.
of this Web Page
There is a mythology about the origin of
scientific investigations regarding any subject.
Cartoons sometimes show someone in a white coat shouting “Eureka
I’ve found it!”
reality, it’s closer to stumbling upon an
unexpected anomaly and not knowing what caused it. (As in a quizzical:
funny?”) This leads to a sequence of questions such as What?,
Why?, etc. Curiosity
about the What?, Why?, etc. is followed by a little research
to try to find
out what is going on and what it might lead to.
The picture above is a Print Screen image of a message that the author
posted in Yahoo’s “Grand Canyon Rafting” Group back in June 2007 – and
now you know the rest of the story.
on the origin of
the name “Pearce Ferry”
“Grand Canyon National
Arizona. Upstream toward the west portal of the Grand Canyon. Note the
ruins of the old stone house in the foreground. This was once one of
the buildings at Pierce (Pearce) Ferry, where a wagon trail from
Kingman to Moapa crossed the river. Colorado River Survey of 1923
The historic photograph above was originally taken
“Colorado River Survey of 1923” and was subsequently
published in the May 1924 issue of National Geographic Magazine. You
can see the original photo at http://libraryphoto.cr.usgs.gov/cgi-bin/show_picture.cgi?ID=ID.%20LaRue,%20E.C.%20%20771
If you click on the photo at the above web link, you can get greater
The estimated location of the photographer is
N, 113.977 W or about 0.63 miles east and a little south of the
developing Superimposition Rapid. (Please see the pin location in the
first Google Earth picture.) The view in the 1923 photograph looks
slightly north of
due east. Based on the estimated location of the photographer and the
location of the river in the photograph, it is estimated that the river
originally turned toward the north just off the left edge of the
photograph, and passed about one-half mile to the east-northeast of the
After Hoover Dam was built, the old river channel
buried under 300 feet of silt and sediments brought down by the
Colorado River. You can get some idea of the magnitude of 300 feet of
sediment by following the ridge that starts in the dark shadow next to
the river and climbs to where it disappears off the right edge of the
photograph. The uppermost portion of this ridge (just off the right
edge) remains barely above the silt flats. If you look at the first
Google Earth picture, you can see a small light-colored “sand
the right and a little below the pin location. The “sand
island” is the top of the ridge that is just off the right edge
1923 photograph. Also, the “sand island” is visible just to
the right of the river in the middle distance in the first 2006 Bureau
of Reclamation photograph.
The picture above was generated by Google Earth
approximately the same view (with slightly wider sides) as the old 1923
photograph, except that as of 2004, the viewpoint is some 300 feet
higher due to the influx of silt. In the Google Earth picture, the low
flat area on the skyline to the left of center appears relatively
higher due to the ~300-foot increase in viewpoint elevation. Most of
the skyline is formed by the inner rim (Grand Wash Cliffs), but the low
flat area is part of the outer rim and is some 5 - 6 miles more distant
(and 1,900 feet higher) than the inner rim. Thus the increase in
viewpoint elevation makes it
appear somewhat higher in the Google Earth view vs. the 1923 photograph.
The name “Pearce Ferry” goes back to 1876 when
Harrison Pearce established a ferry service here to cross the river.
There is good original documentation at:
The spelling of “Pearce Ferry” was
subsequently corrupted to “Pierce Ferry”. (The
“spelling checker” in Microsoft Word didn’t exist
“Pearce Ferry” (also “Pearce’s Ferry”) is
name, “Pierce Ferry” is widely used.
The picture above is a portion of the USGS 1892
Trumbull” topographic map. The river flows from the Grand Canyon in the
lower right corner up toward the upper left corner where it turns left
through Wheeler Ridge before exiting off the upper left edge. The
original of this and other archived USGS maps can be seen at:
USGS maps in 1892 didn’t have anywhere near the
of present day maps, but when you think about it, any reasonably
accurate map in 1892 was a major accomplishment. The old wagon trail
from Kingman to Moapa is marked on the map as well as the location of
Pearce (Pierce) Ferry.
miles 272 to 280
to the Lower Superimposition Rapid page
Index Page for the Grand Canyon Tour
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