Montoya Dolomite (TXOm;0)

State	Texas
Name	Montoya Dolomite
Geologic age	Phanerozoic \| Paleozoic \| Ordovician-Middle Ordovician-Late
Original map label	Om
Comments	(described fr. Van Horn--El Paso Sheet of Geologic Atlas of Texas, 1968) Dolomite, limestone, and sandstone. Upper part--dolomite and ls., aphanitic to medium grained, thin to thick bedded, white to dk dray, cherty. Lower part--limestone and dolomite, aphanitic to v. coarse grained, light to medium gray, local motled zones near base, chert scarce to absent, thin sandstone bed locally at base. Thickness--Franklin Mountains, 250-430 ft; Hueco Mtns 320+- ft; Sierra Diablo, 250-500 ft. Southeastern Baylor Mtns; includes Middle Ordovician Simpson Group rocks not separately mapped. Stratig. divisions used in Orogrande Basin, NM described in Kelley and Silver (1952)
Primary rock type	dolostone (dolomite)
Secondary rock type	limestone
Other rock types	sandstone
Lithologic constituents	Major Sedimentary > Carbonate > Limestone (Bed)thin sandstone bed locally present at base Sedimentary > Carbonate > Dolostone (Bed)
Map references	Bureau of Economic Geology, 1992, Geologic Map of Texas: University of Texas at Austin, Virgil E. Barnes, project supervisor, Hartmann, B.M. and Scranton, D.F., cartography, scale 1:500,000
Unit references	Bureau of Economic Geology, 1968, Van Horn-El Paso Sheet, Geologic Atlas of Texas: Bureau of Economic Geology, The University of Texas at Austin, scale 1:250,000. Udden, J.A., Baker, C.L., and Boise, E., 1916, Texas Univ. Bur. Econ. Geology and Tech. Bull. 44 p. 39. Kelley V.C., and Silver, C., 1952, Geology of the Caballo Mountains: Univ. of New Mexico Publications in Geology, no. 4, University of New Mexico Press.
Geographic coverage	Culberson - El Paso - Hudspeth