Carmen, Sierra del, N spur of the Sierra Madre Oriental in Coahuila, N Mexico, extends c.80 mi/129 km NW from c.28°30'N 102°00'W to the Rio Grande (Texas border) at Big Bend Natl. Park; continued by its U.S. sect. Sierra del Carmen or Carmen Mts. Rises to over 8,924 ft/2,720 m.