Abstract

The Tule Spring Hills are a Basin and Range horst that exposes a structural complex produced by Mesozoic southeastward thrusting and Cenozoic east-west extension. The Tule Spring Hills thrust, eastern kin to the Las Vegas area Keystone thrust, places a 1000-foot- thick (300m) sheet of brittlely fractured, pervasively faulted, Cambrian carbonate strata over less faulted Jurassic Kayenta redbeds and, locally, a melange of Triassic strata. Sandwiched locally between the overthrust Cambrian carbonates and the Mesozoic redbeds are remnant blocks of melanges several thousand feet (m) long, which have been dragged along beneath the thrust plate.

The Lime Mountain thrust places Cambrian and Or-dovician strata over Mississippian limestone, a different sub-thrust stratum than that of the Tule Spring Hills thrust. On the north end of Lime Mountain, the Mississippian limestone is cut by a dike of Miocene volcanic rock and has been locally marbleized. Miocene volcanic rocks, from sources north of the area, originally were laid unconformably across the area but have been removed by erosion, except in a few areas. They include 22 to 24 Ma ash-flow tuffs from the Caliente caldera complex and 10 to 14 Ma tuffs and basaltic rocks from the Clover Mountains just north of the Lime Mountain area.

The north end of the Tule Spring Hills are cut by east-southeasterly trending right-lateral strike-sli faults that appear to offset some of the volcanic rocks and, thus, may be of late Cenozoic age. the major Basin and Range normal faults that bound the Tule Spring Hills are not exposed but have been identified on seismic lines and separate the Tule Spring Hills from the Tule Desert Basin, on the northwest, and the Mesquite Deep Basin on the southeast. The Mesquite Deep Basin contains 32.000 feet (10km) of Tertiary valley-fill in its deepest part, including sediments derived from the Lime Mountain area.