This years trip was another wonderful success! We had a very special group of people who were interested in learning more about the geology of the Grand Canyon from a river perspective. Our guides were accommodating, the weather was splendid, and the muddy river subtly revealed her secrets through time. This is not a complete review of our trip but merely some snapshots of portions of our trip that lasted for 10 days.
September 13 at Lees Ferry had a wondrous sky to the southwest. We received our only significant rain of the whole trip (1/2 hour) later on this evening. The Vermilion Cliffs rise in the background.
Shortly after leaving Lees Ferry, we passed slightly upturned strata that signal the very start of the Grand Canyon. Here is the cream-colored Kaibab Formation just beginning to rise from below the river. Incredible to think that millions of tourists stand on this same stratigraphic horizon 88 miles downstream from here on both the north and south rims. While the river drops an average of 8 feet per mile, the rocks rise out of the ground an average of 70 feet per mile and that is how the high elevations of the tourist areas are achieved. It all starts here.
At about Mile 13, a narrow gorge is cut through the Supai Group rocks.
Our first hike of the trip was up the drainage of North Canyon. This is a very special place with many features of geologic interest.
Rains from the previous evening delivered fresh mud in the stream bed. It looked like chocolate milk.
Another intriguing feature we observed was exfoliation in sandstone. Note how the sandstone spalls parallel to all of the drainages - as the confining pressure is released by the erosion and removal of overlying rock, the sandstone pops out to create these lines of weakness.
Other interesting features observed in the Supai Group are the many root cast from plants that were anchored in the ancient sandy soils. Here is one with the trunk and underlying roots exposed in cross-section.
Alternating beds of cliff-forming sandstone (above) and slope-forming mudstone (below) suggest intervals of climate change during deposition of the Supai Group in the Pennsylvanian Period. The sands may have been deposited in eolian dunes, while the mud may have derived on the muddy floodplain of a river. Here Mark checks out the deposits.
The Grand Canyon and Colorado River always seem to attract unique sporting endeavors. On numerous occasions we passed a world-class surfer who was attempting to paddle the entire length of the canyon on a surfing paddle board. Amazing.
Early morning reflections in the large President Harding loop in the river.
Near the southern end of Marble Canyon, the Bright Angel Shale is beautifully exposed.
I have never seen as many Big Horn sheep as we saw on this trip. A retired BLM biologist, Terry Ruzzi, gladly shared his knowledge of the species with the group. I estimate that we saw over 75 big horn in nine days. Perhaps they were along the river because of unusually dry conditions elsewhere in the canyon.
Not many camps exist in the Inner Gorge of the canyon but we found a nice one at Grapevine Camp across from Vishnu Creek. Everyone enjoyed this ample sandy camp within this beautiful gorge.
Here Gail and Peggy reflect on a days worth of exploration in camp.
Many rapids line the channel of the Colorado and here our group is enjoying the ride in one of the more moderate drops. Most rapids are formed when side canyons deliver boulders to the main channel in big side canyon floods.
In Stephen Aisle, we camped beneath some wonderful Tapeats Sandstone towers. Groundwater most likely weakened the cement of this part of the sandstone but the harder horizons stick out in relief.
Steve, John, and Jim enjoy a quiet moment in camp. These sandy beaches are clean and provide an unbelievably comfortable place from which to watch the sunset in the Grand Canyon.
Peggy relaxing on a boulder in camp.
Here is a view of The Great Unconformity in Blacktail Canyon. The schist below is 1,200 million years older that the sandstone that overlies it. This is more than 1/4th of all earth history.
A rare shot of Bill while not taking a picture on the river. A child-like enthusiasm often overcomes people as they travel down the river.
Within the Middle Granite Gorge are a series of pink dikes that here seem to overwhelm the preexisting black schist. Their patterns are curiosities that beg for photographs.
Islands of rock once stood above a Cambrian sea. I inserted a red line that distinguishes the sea sand (top) from the older rocks that formed high-standing islands (below line). This all happened 525 million years ago.
The temperature of the Colorado River is a cold 48 degrees but many of the side canyons harbor warm, clear water streams. This one is Stone Creek located at about Mile 130.
While returning to Stone Creek beach Mike spotted a Chuckwalla (Sauromalus obesis) sunning on a rock. When alarmed these large lizards will slip into a narrow crack and inflate their lungs with air to wedge inside for protection. Paiute Indians would travel through Northern Arizona with sharp sticks to deflate them and then enjoy a hearty meal.
At only one location in Grand Canyon does a waterfall enter directly into the Colorado River - Deer Creek. This curious setting is the result of a large rock slide that blocked an ancestral Deer Creek, causing it to carve a new route to the river. The new canyon has not yet had time to cut down the grade.
Upper Deer Creek above the falls.
Spectacular view to the east along the Middle Granite Gorge.
This is much the same view as the previous picture but was taken the following morning when smoke from a fire had filled the canyon. We could smell the thick smoke but it lifted later in the day.
The blue water of Cataract Creek in Havasu Canyon. This was a welcome stop away from the muddy river.
As we approached Lava Falls on the river, we spotted a thin black volcanic dike rising up through the stack of sedimentary layers. See if you spot the dike as it rises through the rocks.
A fantastic lava cascade filling a north side canyon.
Look at these beautiful radiating columns within a lava flow. As this lava was cooling, water (either from rain or the river) infiltrated the flow and caused the unique pattern to form.
View of a lava flow remnant along the river.
View south towards Diamond Peak and the Hurricane Fault. The peak is on the downthrown side of the fault - I have inserted a red line to show the approximate trace of the fault. Here as much as 2,000 feet of offset is displayed as the much older Vishnu Schist (left) is placed next to the Muav Limestone (in Diamond Peak).
In the Lower Granite Gorge spectacular fluting in the crystalline rocks is seen. These form when a pebble spins in floods in a small depression, chiseling its way deeper into the bedrock.
A view of the Lower Gorge strata.
The water of Lake Mead is very low right now and deposits of the young "Lake Mead formation" are now being incised by the rejuvenated Colorado River. I once rowed boats on top of these deposits when the lake was much higher.
Here is the new Pearce Ferry Rapid, formed as the river has established a new course across a spur of the consolidated Muddy Creek Formation. This is a nasty rapid that swamped our boat.
After exiting the Grand Wash Cliffs and the western end of the Grand Canyon, all of the previously flat-lying strata are turned up on end. These are most likely deposits of the Supai Group.
I hope you enjoyed this recollection of my last geologic exploration in the canyon. Thanks to the 19 people who took this trip and our three wonderful boatmen from Canyoneers who were so professional in the execution of their craft.