Continued west on Hwy 80 Through Ciudad del Marz when we got cheated by a faulty meter at the Pemex Station. Stopped in an acacia lined ravine 8.0 miles west of Col.del Mari to look for Amely tropisus. Saw only Cnemidophorus. Took photos of the habitat. Later started getting into a more desert-like habitat on the flats of the plateau and stopped along the side of the road (Mex. Hwy 80) several times as follows to look under yucca logs. 0.4 miles E. La Morena San Luis Potosi via Hwy. 80. A desert-like area with much Thorn scrub on the south side of the road and cultivated- or at least plowed- land on the north side. Looked for roosting yucca trees on the right of way on the north side of the road. 67 Sceloporus cautus from under a fallen, rotting yucca log. Another was seen but escaped. When chilled has virtually no chromatic color any place of head or body. Cnemidophorus Several seen