Cuesta La Muralla

“Cuesta La Muralla” refers to the pass through the Sierra La Gavia  along Mexican Highway 57 that runs north from Saltillo to Monclova.  This range is one of a number of northwesterly aligned, mountain-forming anticlinal structures which constitute part of the Coahuila Marginal Folded Province of northeastern Mexico.  The range is roughly 60 miles in length, rising abruptly out of the bolsón plains that border its northeast and southwest flanks.  Lower-Upper Cretaceous-Quatrernary rocks exposed within the Sierra include several thousand feet of sedimentary rocks.  Lower Cretaceous formations, which are more than 7000 feet thick, form the major part of the mountain mass.  Although a number of alterna have been found here, most were DORs, a consequence of the high traffic volume typical of this road.  It is a dangerous place to road hunt, especially at night.  The region has produced both blairi and alterna morphs, as well as intermediates.  Additional images are available on the Alterna Page.  All photos copyright Troy D. Hibbitts.  (August 2007).