Whitmore Canyon Overlook - Whitmore Point - Frog Spring
These road descriptions refer to the main visitor routes south of the Mount Trumbull schoolhouse. Roads are listed in numerical order. Use this guide with the BLM Arizona Strip Visitor Map. Most roads in this area should be explored with a high clearance four wheel drive vehicle with all-terrain tires in good condition at a minimum. However, some roads are only suitable for UTVs or specially modified short wheelbase 4x4s.
This is not a complete guide to all roads in the Whitmore Canyon area. This list includes numbered and unnumbered roads on the BLM map that are used by the recreating public frequently. For all other roads assume they are for specially modified short wheelbase 4x4s. Some are only for UTVs. Always turn around if it gets too rough for your vehicle.
Whitmore Canyon's Dramatic VolcanismAfter a long rough drive out to Whitmore Point visitors are treated to a stunning view of a seldom visited part of the Grand Canyon. But as you can see from the photo, ancient cinder cones and several lava flows decorate this part of the Grand Canyon too.
Whitmore Canyon is at the southern end of the Uinkaret Plateau, which sits over a large magma chamber only a few miles below the surface. If the magma wasn't there, the Uinkaret Plateau would be 2,000 feet lower in elevation. This magma chamber still erupts from time to time. Unlike Cascade Mountain volcanoes like Mt. St. Helens with its massive roiling grey pyroclastic eruptions, which is caused by a large amount of water in the magma that can explodes into steam, this magma is dry and isn't nearly as explosive. The lava flow events in Whitmore Canyon vary in age from 87,000 years to around 530,000 years ago.
So what would you have seen if you were standing here during one of these lava events? For months beforehand, earthquakes shook the ground. Then a long crack formed on the far hill in the photo. Out flowed lava, perhaps in a mile long fountain that shot red hot rock a thousand feet in the air. Then the lava began to flow downhill. Imagine watching the advancing wall of lava from Whitmore Point. You would have heard the scraping grumble of stone as a rolling front of lava poured into the valley. Grass fires would have raced up the slopes to Whitmore Point as the 2,000 degree lava headed downhill toward the Colorado River. When the lava reached the lowest rim of the canyon at the overlook, still 1,000 feet above the river, a cascade of red syrupy magma, like molten glass, dropped into the river. Steam blasts would have echoed like cannon-fire off canyon walls for miles around as hot rocks exploded in the cold water. As the lava filled the river bottom, the rushing waters of the Colorado boiled away in a billowing cloud of steam.
When the lava stopped flowing, a lava dam, perhaps 600 to 1000 feet high, plugged the base of the canyon. This formed a new lake. The lava kept flowing several miles downstream. This meant that for weeks or even months after the flow stopped, the Colorado River downstream of Whitmore Canyon was dry. Only small tributary streams below the lava dam added their meager waters into the riverbottom. For at least few months the Colorado River would have been dry all the way to where the Muddy River near Overton, Nevada, flows into the Colorado.
The lake that formed behind the dam took only a few years to fill, eventually stretching 50-100 miles upstream somewhere between Phantom Ranch and where the Little Colorado River joins the Colorado River. Had this happened in modern times, visitors at the South Rim in Grand Canyon National Park would have looked down at first on a vast lake in the canyon. After about 200 years as the river filled the lake with sand and silt, the lake would have been transformed into a broad, flat forested plain full of willows and cottonwoods. The Colorado River would have meandering slowly over this plain toward the lava dam and its terrible cataracts.
This dam is mostly gone today. Geologists aren't sure if the lava dam lasted only a few decades or several thousand years, but still, lava makes for a weak dam even if it was several miles thick. The water would have eventually found ways through the jumble of poorly cemented basalt and come out the other side. It could have slowly eroded the dam from within as silty water scraped open wider and wider passages and it slowly collapsed on itself. Or, the river may have poured over the top making a series of dramatic cascades where crashing water broke away bits of basalt day after day. Scientists aren't sure if it was one way or the other, or perhaps both. Either way, the power of the water eventually weakened the dam to the point of failure.
One day the dam collapsed and a massive slurry of water, clay, and boulders roared past Whitmore Canyon toward the Pacific Ocean. Upstream of the dam, a deep gorge would have been cut in the loose material of the broad plain within hours, all the way back to the Little Colorado River. Everything fell into the sandy gorge. The flood would have been filled with perhaps millions of cottonwoods and willows that once covered the sandy plain as the Colorado cut fast through the loose soil behind the destroyed dam. River-rounded limestone boulders, some over 40 feet in diameter, are found mixed with sand and gravel far downstream. Only a huge outburst flood could have smoothed the boulders like that and rolled them so far. For years the river could have been choked with mud as centuries of silt, sand, and gravel were eroded by the river and summer rainstorms. After the flood subsided, some basalt still clung to the cliffs. As time passed, the weight of the remaining chunks of basalt caused the boulders to break off and fall into the river. This created the adventurous rapids that raft trips navigate today.
This was just one of over a dozen of these dams at different places in the Grand Canyon. One lava dam that flowed out of Prospect Canyon, just across the river from Toroweap, happened about a half million years ago. It was so high the lake it made stretched clear into Utah and contained vastly more water than Lake Mead and Lake Powell combined.
The Uinkaret Plateau remains volcanically active. A new eruption could happen at any time. The last eruption was only 1,050 years ago at Little Springs by Mt Trumbull. This is just a few miles from Whitmore Canyon. Magma plumes are rising right now, but it could be thousands of years before the next eruption adds its decoration to this landscape.
If you would like to learn more about Grand Canyon volcanism, information here was summarized from this publication from the Geological Society of America.
Last updated: April 17, 2018