Blackhawk landslide, southwestern San Bernardino County, California

Abstract The Blackhawk landslide is located in southeastern Lucerne Valley at thesouthern edge of the Mojave Desert 85 mi (135 km) east of the Los Angeles, California, civic center. It lies across the eastern half of the line separating the Cougar Buttes and Big Bear City, California, U.S. Geological Survey7½-minute Topographic Quadrangles. Its distal (lower) end is readily apparent on both the map and the ground near 34°25'N, 116°47'W. The easiest way to reach the landslide is to take I-15 to Victorville, then California 18 east through Apple Valley, approximately 25 mi (40 km) tothe center of the town of Lucerne Valley, and finally County Highway 247 (CH247, Fig. 1) east 8.7 mi (13.9km) to its intersection with Santa Fe Road (SFR, Fig. 1). The steep, gray, 50-ft (15-m) scarp approximately 2,000 ft (600 m) to the southeast is the distal edge of the landslide. It can most conveniently be visited on foot either from the prospectors' road (moderate clearance or four-wheel drive advisable) that enters the highway at Santa Fe Road or from the highway itself about 0.6 mi (1.0 km) farther east. Features along the west side of the landslide can be reached along Blackhawk Canyon Road (BCR, Fig. 1; moderate clearance or four-wheel drive advisable), which crosses the highway 1.05 mi (1.7 km) west of the Santa Fe Road intersection. Features within the landslide lobe can be reached by taking Blackhawk Canyon Road south from the highway 1.05 mi (1.7 km) to the remains of a jeep trail that goes eastward, following it (four-wheel drive strongly advisable) to the dry wash nearest the landslide, and driving up the wash. Alternatively, these features can be visited on foot by hiking from the roads to the west and south. Features of the proximal (upper) part of the landslide can best be reached by taking County Highway 247 east from the Santa Fe Road intersection 3.25 mi (5.2 km) to a well-graded mine road marked by a large white marble boulder, then taking the mine road (low hill on right 4.4 mi (7. 1 km) from highway is eastern lateral ridge of Silver Reef landslide) southwest 5.3 mi (8.5 km) to a prospectors' road (intersection about 1,400 ft (425 m) northeastof Round Mountain), next taking the prospectors' road (moderate clearance or four-wheel drive advisable) west approximately 0.25 mi (0.4 km) to where it crosses another similar road, and finally taking the other road northwest 1.6 mi (2.6 km) to the mouth of Blackhawk Canyon (BCM, Fig. 2). Features in the vicinity can be visited either on foot or, in most cases if road conditions permit, by vehicle (moderate to high clearance and low gear or four-wheel drive advisable). Good views of the landslide lobe on the alluvial slope and of its source area on Blackhawk Mountain can be obtained from the mine road (high clearance and low gear or four-wheel drive strongly advisable) that climbs the ridge just east of Blackhawk Canyon (VP, Fig. 2).