Geology from a Motor Car 337 



winds. Clumps of vegetation serving as anchors have caught 

 the drifting sands and caused the mounds to form. 



Across the Peninsular Range 



The route is across the Peninsular Range of mountains. 

 LaMesa, 11 miles from San Diego, is 539 feet above sea level. 

 El Cajon Valley (17 miles) is slightly lower (450 feet), with 

 Mount Helix rising conspicuously south of the highway. The 

 mesa floor rises again to 490 feet at Bostonia (19 miles) . Wind- 

 ing over a fine mountain highway Alpine (31 miles) is reached 

 at an altitude of 1,860 feet. The mountain climb continues to 

 3,540 feet at Descanso (43 miles). Proceeding east, a few 

 miles to the north is Cuyamaca Peak (altitude 6,515 feet), and 

 immediately south of the highway is Gautay Mountain (5,300 

 feet) . Here is the axis or summit of the Peninsular Range, 

 and the descent of the eastern slope begins. The elevation at 

 Laguna Jet. (49 miles) is 4,050 feet. Turning southeast in 

 Cottonwood Valley the eastern fault scarp of the Laguna 

 Mountain range stands boldly out on the west. Swinging far 

 south around the south end of the Laguna Mountain range, 

 crossing McCain's Plateau, Jacumba is reached (2,800 feet; 76 

 miles) , one-half mile north of the Mexican Boundary. To the 

 north is Carrizo Gorge, which is followed by the railroad but 

 not by the highway. The gorge is eroding its way backward 

 into the soft Tertiary sediments from the north end of Jacumba 

 Valley. After passing Smugglers' Cave, turn north and pause 

 for a look at the rocks in Boulder Park, at the foot of the 

 Jacumba Mountains. Jacumba Valley is a faulted valley, and 

 withal has been overwhelmed by outpourings of volcanic lavas. 



Points of Interest on East Slope 



Take time to enjoy Inkopah Gorge after passing Boulder 

 Park and Mountain Springs Park. Stop and take a drink at 

 Coyote Wells, and turn south and visit the Petrified Forest if 

 time will permit. It will not be possible to see everything that 



