The Topia Road: A Trans-Sierran Trail of Colonial Mexico

Abstract

FIG. i-Colonial roads in western Mexico. Key: I, West Coast-Interior Plateau connections; 2, West Coast Road (from C. 0. Sauer: Road to Cibola, Ibero-Americana, 3, Berkeley, I932); 3, Western Interior Plateau Road; 4, connections northward from Guadalajara. The Sierra Madre Occidental presents one of the most formidable obstacles to land transportation in Mexico. Throughout its length of 750 miles, from a point near the United StatesMexico boundary in the north to the Santiago River in the south, no railroad, auto road, or cart trail has ever traversed this barrier. Since colonial days only a few pack trails across the Sierra have served as direct lines of land contact between the Pacific coastal areas and the interior plateau of northern Mexico. The Sierra Madre is a plateau, I00 to I50 miles wide, with a steep western escarpment. It represents the higher western edge of the great Mexican plateau. Outflows of Tertiary extrusives, accompanied by uplift, have raised the Sierra to a general altitude of 8ooo feet above the sea, and some I500 to 2000 feet above the adjacent parts of the interior plateau; only isolated sections reach altitudes above I0,000 feet. The eastern part is characterized by a slightly rolling surface dotted with mountain meadows occupying the shallow north-northwest-south-southeast structural depressions. This part presents few difficulties to land transportation. To the west, however, the headward erosion of the streams flowing to the Pacific has cut deep box canyons into some parts of the plateau surface. These precipitous canyons, 8oo to I000 feet deep, are more numerous near the western edge of the highlands and impose serious handicaps on even mule transport. However, the most formidable barrier is the steep western escarpment, known as the barrancas. Scores of large westward-flowing streams have frayed this escarpment with enormous canyons, or barrancas, 2000 to 3000 feet deep, producing some of the most rugged terrain in Mexico. Pack trails must follow either the 406