SOUTHERN PACIFIC LINES 89 
Another outstanding promontory lies south of Tesnus and comes 
into view a short distance beyond Maxon. Merging into the plateau 
near Maxon at an elevation of 3,700 feet, in 6 miles it rises considerably 
higher to its western termination, where it breaks into three peaks 
known as Tres Hermanas, each capped by a small mass of Edwards 
limestone. The ridge stands 1,300 feet above the plains to the north, 
but its steep southern front rises 2,000 feet above the valley of San 
Francisco Creek. 
The sharp ridges of the basin, underlain by hard rocks, extend 
across it in a northeastward direction. Some of them run nearly 
straight for many miles; others have a winding course, as shown in 
Plate 13, B, expressing the complex deformation of the strata. On 
many of the ridges are ledges of white siliceous rock called novaculite. 
Between the ridges are wide valleys covered by soil and gravel, but 
along the larger drainage ways the land is cut by many arroyos into 
a maze of terraces and shallow, steep-walled valleys. Much of the 
Basal shale member of Tesnus 
ue 
Om SEnYs(ssr:7 Dp 
Devonian (?) nevaculite 
4 Miles 
FIGURE 10.—Section through House Mountain, about 1 mile north of the railroad northwest of 
‘Tesnus, Tex. 
terrace gravel consists of white novaculite and has the appearance 
of drifted snow. 
West of Tesnus Horse Mountain is prominently in view 10 miles to 
the southwest. This is the highest peak in the Marathon Basin 
(elevation 5,010 feet) and is a dome-shaped mass of novaculite of 
anticlinal structure. The railroad crosses a level plain for several 
miles west of Tesnus and then descends into a region of hills and 
valleys, drained by San Francisco Creek.* 
Within the Marathon Basi the| ‘A few miles beyond Tesnus the 
Paleozoic rocks constitute low, sharp | railroad crosses a fault, not visible from 
ridges far inferior in magnitude to the | the tracks but well exposed some miles 
mountains that must have existed when | to the north and south, which brings 
the folding of later Paleozoic time took | the Tesnus strata the 
place. The et low ridges were part of the Haymond formation occu- 
produced by beige n post-Cretaceous | pying a syncline. The highest exposed 
time, after o Mantle dome was | member of this Pink e. also con- 
uplifted and ae Cretaceous rocks wi cealed by gravel near the railroad but 
eroded from the area of the iMawicg well exposed in slopes not far away, is 
Basin. a remarkable conglomerate con ntaining 
152109°—33——7 
