GEOLOGIC SUMMARY adjoins the eastern border (Billingsley and Hampton, 2000). by George H. Billingsley The Mount Trumbull 30´ x 60´ quadrangle encom- The geologic map of the Mount Trumbull 30´ x 60´ passes approximately 5,018 km2 (1,960 mi2) of land quadrangle is a cooperative product of the U.S. Geologi- within Mohave and Coconino Counties of northwestern cal Survey, the National Park Service, and the Bureau of Arizona. The quadrangle is bounded by longitude 113° to Land Management that provides geologic map coverage 114° and latitude 36°00´ to 36°30´. Elevations within the and regional geologic information for visitor services map area range from 2,447 m (8,028 ft) at Mount Trum- and resource management of Grand Canyon National bull on the Uinkaret Plateau, northeast quarter of the map Park, Lake Mead Recreational Area, and Grand Canyon area, to 353 m (1,156 ft) at Lake Mead, southwest quarter Parashant National Monument, Arizona. This map is a of the map area. compilation of previous and new geologic mapping that The map area lies mostly within the southwest- encompasses the Mount Trumbull 30´ x 60´ quadrangle ern part of the Colorado Plateau and partly within the of Arizona. southeastern edge of the Basin and Range geologic prov- Dutton (1882) made the first early reconnaissance inces. The Colorado Plateau is locally subdivided into geologic map of the Uinkaret Plateau, which is part of seven physiographic areas as shown by Billingsley and this map area. More recently, Huntoon and others (1981, others (1997): the Grand Canyon, the Kanab, Uinkaret, 1982) and Billingsley and Huntoon (1983) produced geo- Shivwits, and Sanup Plateaus north of Grand Canyon, logic maps of the south half of this area that were later and the Coconino and Hualapai Plateaus south of Grand revised by Wenrich and others (1996, 1997). Geologic Canyon (fig. 1). The approximate position of the Grand maps within the north half of the map area were produced Wash Fault separates the Basin and Range province from by Lucchitta and Beard (1981a, b), Billingsley (1997a, the Colorado Plateau province. The northwest part of the b, c), Billingsley and others (2000), and Billingsley and map area is referred to as the Grand Wash Trough within others (2001, 2002, unpub. data). A geologic map of the the Basin and Range (fig. 1). Littlefield 30´ x 60´ quadrangle borders the northern The boundary between the Kanab and Uinkaret edge of this map (Billingsley and Workman, 2000) and a Plateaus is marked along the Toroweap Fault, which is a geologic map of the Grand Canyon 30´ x 60´ quadrangle geologic and topographic feature. The boundary between 114°00' 113°00' 36°30' U UINKARET PLATEAU U TEA Mount Trumbull U TROUGH T TEA L PLA U TEA A PLA U Bundyville F TEA (Mount Trumbull) WASH H Tuweap S SHIVWITS PLA A W KANAB PLA D GRAND N A R AND RANGE G r ive R o rad COLORADO olo SANUP U C BASIN Mount Dellenbaugh TEA PLA C olo rado R i v SANUP COCONINO HUALAPAI e r PLATEAU PLATEAU 36°00' Figure 1. Index map of the Mount Trumbull 30' x 60' quadrangle, Arizona showing the physiographic provinces and subprovinces. 1 the Uinkaret and Shivwits Plateaus is marked along the are exposed at the bottom of Grand Canyon along a one- Hurricane Fault that forms the Hurricane Cliffs, a promi- mile reach of the Colorado River between Miles 189.6 nent west-facing fault scarp. The boundary between the and 190.6 as measured from Lees Ferry, Arizona. The Shivwits Plateau and Sanup Plateau is marked along the majority of the map area is characterized by gently east north rim of the Grand Canyon and northward along the and northeast dipping Paleozoic and Mesozoic strata that upper Grand Wash Cliffs to Hidden Canyon. The Sanup overlie Early Proterozoic crystalline metamorphic rocks. Plateau is a narrow flat platform or topographic bench Paleozoic rocks comprise most of the cliffs and between the north rim and the inner gorge of the Grand slopes in the walls of Grand Canyon and display remark- Canyon and between the upper and lower Grand Wash able east-west facies and thickness changes. The Perm- Cliffs. The Sanup Plateau extends to the Hurricane Fault ian Kaibab Formation (Pk) generally forms the rim of at Whitmore Canyon. Grand Canyon north and east of the Colorado River and The nearest settlements to the map area are Colorado the plateau surface of the Shivwits, Uinkaret, Kanab, and City, Arizona about 58 km (36 mi) north of the northeast Coconino Plateaus because of its resistance to erosion. corner of the map area, and St. George, Utah about 90 However, the Kaibab Formation has been removed along km (56 mi) north of Mount Trumbull. There are two the southern part of the Shivwits Plateau due to Laramide abandoned settlements within the map area, Tuweap and uplift and subsequent erosion allowing the Toroweap Mount Trumbull (fig. 1). The town of Mount Trumbull, Formation (Pt) to form the canyon rim in some areas. A locally known as Bundyville, is near the base of the Hur- significant unconformity separates the Kaibab Formation ricane Cliffs on the Shivwits Plateau about 16 km (10 mi) from the underlying Permian Toroweap Formation. Chan- west of Mount Trumbull mountain. Today, Bundyville is nels as much as 43 m (140 ft) deep have eroded into the little more than a small cluster of local ranches and one soft strata of the Woods Ranch Member of the Toroweap abandoned historic schoolhouse. Tuweap is in the upper Formation in Toroweap, Whitmore, and Mohawk Canyon reaches of Toroweap Valley, a northern tributary to Grand areas. Otherwise, the Toroweap Formation maintains a Canyon consisting of a few abandoned ranch buildings. general overall thickness throughout the map area. The Toroweap Campground is in Grand Canyon National limestone of the Brady Canyon Member of the Toroweap Park in the lower reaches of Toroweap Valley on the rim Formation thickens from east to west while sandstone of the inner gorge of Grand Canyon and provides a spec- and gypsum of the Seligman Member thins from east to tacular overlook of the Colorado River (Colorado River west. The Permian Coconino Sandstone (Pc) intertongues Mile 174 to 183). within the lower part of the Seligman Member of the Access to the plateau regions north of Grand Canyon Toroweap Formation (Pt) in the vicinity of Parashant and is by dirt roads that are maintained by the Bureau of Whitmore Canyons (Fisher, 1961; Schleh, 1966; Rawson Land Management of the Arizona Strip Field Office in and Turner, 1974; Billingsley and others, 2000). Because St. George, Utah. Access to the Coconino and Hualapai the name Coconino Sandstone is well established in the Plateaus in the southwestern and southeastern part of the Grand Canyon nomenclature and it forms a significant map area is by jeep trails and dirt roads maintained by mappable cliff unit within the walls of Grand Canyon, the Hualapai Tribe and requires permits from the Tribe the Coconino Sandstone is herein maintained as a sepa- for access and travel. Access into the depths of Grand rate map unit. The Coconino Sandstone unconformably Canyon in this map area is rather limited to a few non- overlies the Hermit Formation and pinches out in the maintained trails and a go-at-your-own-risk type of west third of the map area, which allows the Toroweap hiking. Visitors north of the Colorado River must obtain Formation to overlie the Hermit Formation. The Permian hiking permits and information from the backcountry Hermit Formation (Ph) undergoes a facies change from a office at Grand Canyon National Park, Grand Canyon deltaic siltstone and sandstone sequence in the east quar- Village, Arizona, or from the Toroweap Ranger Station ter of the map area to a thicker marine-shoreline sand- in Toroweap Valley. Visitors south of the Colorado River stone and siltstone sequence in the west quarter of the must obtain permits from the Hualapai Tribe at Peach map area. A regional unconformity separates the Hermit Springs, Arizona. Formation from the underlying Esplanade Sandstone, but the unconformity is difficult to locate in the map area because the erosional relief is little more than 3 m (10 ft) GEOLOGIC SETTING at the top of a sandstone ledge about 60 m (200 ft) above Erosion by earlier Laramide and Tertiary streams the sandstone bench of the Sanup Plateau in the Grand and the Colorado River and its tributaries have exposed Wash Cliffs area and in Parashant Canyon. about 365 m (1,200 ft) of Mesozoic strata, over 1,220 m The Supai Group (McKee, 1982) includes, in (4,000 ft) of Paleozoic strata, and about 30 m (100 ft) of descending order, the Esplanade Sandstone, Wescogame Early Proterozoic crystalline metamorphic rock complex Formation, Manakacha Formation, and Watahomigi For- within the map area. The Early Proterozoic rocks (Xgr) mation. The Permian Esplanade Sandstone of the Supai 2 3 Group (Pe) is composed of an upper siltstone slope unit, The Mississippian Redwall Limestone (Mr) gener- a middle sandstone cliff unit, and a lower siltstone and ally maintains a constant thickness throughout the map sandstone slope unit near and east of the Hurricane Fault. area except where removed by erosion in Late Missis- However, west of the Hurricane Fault, the middle sand- sippian time. The Redwall Limestone consists of marine stone cliff unit intertongues with marine limestone beds limestone and dolomite beds that form a major gray cliff of the Pakoon Limestone between the Grand Wash Cliffs throughout the Grand Canyon area. The Devonian Temple and the Hurricane Fault.