Page 174 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

MINING DISTRICTS 171
in the reports of Clark and Gordon, but he has included data obtained during his study of the surface geology and the detailed examinations of several small recent underground workings.
The district is in the southwestern part of Sierra County and is about 7 miles from both the western and southern bound- aries. This is the only mining district in the county having a direct rail connection, which is by way of the 13-mile branch line out of Nutt, a small station on the Rincon-Deming-Silver City branch of the Atchison, Topeka & Santa Fe railway. The town of Lake Valley owes its present slight activity almost entirely to the fact that this rail connection makes it the distrib- uting and shipping point for nearly the entire southwestern quarter of Sierra County and adjacent parts of Luna and Grant counties. The district is not a large one, the entire known mineral-bearing area being within a rectangle three-quarters of a mile long in a northeasterly direction and half a mile wide. The old Santa Fe trail is reported by Clark57 to have passed within 6 miles of Lake Valley, and the camp is 15 miles in an air line from the Rio Grande.
GEOGRAPHY
The immediate vicinity of Lake Valley is an area of low hills
and basins, which are surrounded by higher peaks and ridges partly enclosing the terrane on three sides but opening to the southeast and south onto the great alluvial plain that extends through the length of the county along the west bank of the Rio Grande and to Deming and beyond. The most prominent topo- graphic features of the region are two rhyolite peaks, Porphyry Hill 1 mile southwest of Lake Valley and the so-called Rhyolite Range 3 miles northwest. Porphyry Hill attains an elevation of 1,000 feet and the Rhyolite Range about 1,500 feet above the town. About a mile to the east is Monument Peak, an isolated knob that overlooks the town from an elevation of 500 feet. This group of hills marks the termination of a short, rapidly dwindling spur which diverges from the main Black Range in a south- easterly direction to disappear under the detrital material of the valley plains bordering the Rio Grande at a point just east of the town. Within the basin a ridge of sedimentary rocks trends northeast with gradually decreasing elevation, until it disappears under the detrital material near the former lake that gave the district its name. Lake Valley lies on the southeast or dip-slope side of this sedimentary ridge. Due to the presence of alternat- ing strata of hard limestones and softer shales, the dip slope of this tilted block has been eroded into a series of alternating troughs and cuestas. Apache Hill, due north of the town, is the high point of the sedimentary ridge, rising to an elevation of more than 700 feet above the mines. Surrounding the ridge and in the erosional troughs on its dip-slope side, alluvial material
57Clai.k, Ellis, op. cit., p. 132.