A depositional-tectonic model is proposed for the reconstruction of a Miocene lacustrine basin in the southern Las Vegas Range, Nevada, that was fragmented during a period of extensional tectonism. The model suggests that the sediments were deposited in an isolated basin during initiation of normal faulting in the Sheep Range extensional allochthon 12 to 16 Ma. After 12 Ma, deposition in this basin was terminated by normal faulting followed by oroflexural rotation along the Las Vegas Valley shear zone; The unique Middle Miocene sequence is 335-m-thick and consists of interbedded nonmarine limestone, siltstone, sandstone, conglomerate, megabreccia, and volcanic ash. The formation represents deposition in a shallow, permanent lake 12 to 16 Ma. Post 12 Ma, the formation was faulted by north-striking, normal faults. Subsequently, oroflexural bending along the Las Vegas Valley shear zone, rotated the faults into their present northeast-striking orientation
