The Sierra de Parras lies in southern Coahuila, directly south of the Parras Basin. It begins, on the west, near Puerto La Peña, about 60 miles east of the city of Torreón, and extends east-southeast about 100 miles, as a distinct, rugged topographic unit, finally merging into the ranges of the Sierra Madre Oriental, in the region south of Saltillo.
The area mapped extends from Puerto La Peña eastward 26 miles to about 4 miles east of Parras. It comprises about 370 square miles, of which only 260 are mountainous. The width of the mountainous area varies considerably, being 5 miles near La Peña, 12 miles about 10 miles farther east, and 9 miles in the region south of Parras. Its shape is extremely irregular.
Available maps of southern Coahuila are on a scale of 1 to 500,000 and . . .