Toroweap Point, a remote overlook on the North Rim of the Grand Canyon, offers one of the most dramatic geological cross-sections in the world. The location is characterized by a sheer, abrupt drop where the canyon is exceptionally narrow, measuring less than a mile across to the South Rim. This unique physical characteristic allows geologists to observe complex processes, including recent volcanism and deep-seated structural forces. The landscape here is unlike the wider, more tiered eastern canyon, presenting an abrupt gorge. The findings at Toroweap provide a localized understanding of the forces that have shaped the canyon during its more recent history.
Evidence of Recent Volcanic Activity
The most striking geological findings at Toroweap Point relate to the region’s recent volcanic history. This area sits within the Uinkaret Volcanic Field, which has seen eruptions from approximately 7 million years ago up to the geologically recent past. The landscape is studded with black cinder cones, such as the prominent Vulcan’s Throne, which sits directly on the brink of the inner gorge. These eruptions produced extensive floods of basaltic lava, which are more durable than the surrounding sedimentary rock.
Over 50 individual lava flows have filled the nearby Whitmore Canyon, and Toroweap Valley itself is filled by 18 lava flows to a depth of 3,000 feet. The most significant geological event was the formation of lava dams, where basalt poured over the canyon rim and cascaded into the gorge, temporarily blocking the flow of the Colorado River. Geologists have identified at least 13 separate lava dams that formed during the Pleistocene Epoch, between about 1.8 million and 400,000 years ago.
The evidence for these dams is found in remnants of hardened basalt clinging to the canyon walls and in lacustrine (lake) sediments deposited behind the former lava barriers. The Colorado River rapidly eroded these dams, often within a few thousand years, re-establishing its course. The most recent major lava outpouring into the canyon occurred an estimated 72,000 years ago.
Defining the Canyon’s Structure: The Toroweap Fault System
The narrow geometry of the canyon at Toroweap is structurally controlled by the Toroweap Fault, a major tectonic feature in the region. This fault is part of a system, along with the Hurricane Fault, that is among the most active in Arizona. The fault line runs directly through the Toroweap Valley and crosses the Colorado River, continuing south into Prospect Canyon.
The Toroweap Fault is a normal fault, meaning the block of rock on one side has moved downward relative to the other side, causing significant displacement. This structural weakness along the fault line created a zone of fractured rock that was more easily eroded by the Colorado River, contributing to the deep incision seen at this point. The movement on these faults has been active over the past two to three million years. This ongoing structural movement also influenced the volcanic activity, as the fault provided a pathway for magma to rise to the surface and feed the eruptions.
Reading the Rock Layers: A Unique Stratigraphic Cross-Section
The exposure at Toroweap provides geologists with a clear view of the canyon’s stratigraphic sequence, which chronicles hundreds of millions of years of Earth history. The layered Paleozoic rocks that form the temples and buttes of the eastern canyon are visible here, although the profile is dominated by massive limestone cliffs. The stratigraphy includes the Permian-aged Kaibab Limestone at the rim, underlain by the Toroweap Formation, and the Coconino Sandstone.
A significant finding here is the thickening of the Hermit Shale to the west, which swells to 800 feet in the Toroweap area. The erosion of this softer, thicker Hermit layer created the broad, flat area known as the Esplanade Platform, a major landform in this part of the canyon. Geologists use the Toroweap exposure to correlate these rock units and understand the regional geological history. These layers record extensive marine environments, with the Toroweap Formation representing a transition from coastal dunes to a shallow, marine tidal flat.