|Abstract:||The geologic map of part of the Uinkaret Volcanic Field is one product of a cooperative project between the
U.S. Geological Survey, the National Park Service, and the Bureau of Land Management to provide geologic
information about this part of the Grand Canyon-Parashant Canyon National Monument of Arizona. The Uinkaret
Volcanic Field is a unique part of western Grand Canyon where volcanic rocks have preserved the geomorphic
development of the landscape. Most of the Grand Canyon, and parts of adjacent plateaus have already been mapped.
This map completes one of the remaining areas where uniform quality geologic mapping was needed. A few dozen
volcanoes and lava flows within the Grand Canyon are not included in the map area, but their geologic significance to
Grand Canyon development is documented by Hamblin (1994) and mapped by Billingsley and Huntoon (1983) and
Wenrich and others (1997). The geologic information in this report may be useful to resource managers of the Bureau
of Land Management for range management, biological, archaeological, and flood control programs.
The map area lies within the Shivwits, Uinkaret, and Kanab Plateaus, which are subplateaus of the Colorado
Plateaus physiographic province (Billingsley and others, 1997), and is part of the Arizona Strip north of the Colorado
River. The nearest settlement is Colorado City, Arizona, about 58 km (36 mi) north of the map area (fig. 1). Elevations
range from about 2,447 m (8,029 ft) at Mount Trumbull, in the northwest quarter of the map area, to about 732 m (2,400
ft) in Cove Canyon, in the southeast quarter of the map area. Vehicle access is via the Toroweap and Mount Trumbull
dirt roads (fig. 1). Unimproved dirt roads traverse other parts of the area except in designated wilderness. Extra fuel,
two spare tires, and extra food and water are highly recommended for travelers in this remote area.
The U.S. Bureau of Land Management, Arizona Strip Field Office, St. George, Utah manages most of the area.
In addition, there are 12 sections belonging to the State of Arizona, about 12 sections are private land, and several
sections are within the Grand Canyon National Park and Lake Mead National Recreational Area (U.S. Department of
the Interior, 1993). The private land is in Potato Valley and Lake Valley, southwest and west of Mount Trumbull, and
in Whitmore Canyon and Toroweap (Tuweap) Valley. Portions of the Sawmill Mountains, Mount Logan, and Mount
Trumbull areas were originally established as part of the Dixie National Forest in 1904. In 1924, Dixie National Forest
land became part of the Kaibab National Forest. Then on February 13, 1974, management of this part of the Kaibab
National Forest was transferred to the Bureau of Land Management, Arizona Strip Field Office (personal commun.
Becky Hammond, Bureau of Land Management, 1997). Mount Logan and part of the Sawmill Mountains are now
designated as the Mount Logan Wilderness Area, and Mount Trumbull is designated as the Mount Trumbull Wilderness
Area. Most of the map area is now part of the new Grand Canyon-Parashant Canyon National Monument established
January 11, 2000.
Lower elevations within Hells Hollow, Whitmore Canyon, Toroweap Valley, and Cove Canyon support a
sparse growth of sagebrush, cactus, grass, and a variety of desert shrubs. Sagebrush, grass, cactus, cliffrose bush, pinion
pine, and juniper trees thrive at elevations above 1,830 m (6,000 ft). Ponderosa pine and oak forests thrive at higher
elevations in the Mount Trumbull and Mount Logan areas.
Surface runoff within the map area drains south towards the Colorado River through Hells Hole, Hollow,
Whitmore Canyon, Toroweap Valley, and Cove Canyon. Upper Toroweap Valley, upper Hells Hollow, and Whitmore
Canyon are part of the physiographic area of Grand Canyon, but are not within Grand Canyon National Park
(Billingsley and others, 1997). As of January 11, 2000, these areas are now part of the new Grand Canyon-Parashant