For about 40 miles from near Pagosa Junction to Durango, the Byway follows closely the path of the Northern Route of the Old Spanish Trail. Up until 1848, southern Colorado was still part of Mexico. Traders in Santa Fe, the capital of Nuevo Mexico, needed a route to reach the then remote Mexican settlement of Los Angeles. Over time, a number of routes were developed. The 700-mile Northern Route, also called the Main Route, was first traveled in 1830 by a party led by William Wolfskill and George Yount. This route ran northwest from Santa Fe through southwestern Colorado, past the San Juan Mountains, entering Utah near present-day Monticello.
Commerce usually consisted of one annual mule pack train from Santa Fe with 20 to 200 members, with roughly twice as many mules, bringing New Mexican goods hand-woven by Indians, such as serapes and blankets, to California. California had many horses and mules, many growing wild, with no local market, which were readily traded for hand-woven Indian products. Usually, two blankets were traded for one horse; more blankets were usually required for a mule, which were considered hardier. California had almost no wool-processing industry and few weavers, so woven products were a welcome commodity. The trading party usually left New Mexico in early November to take advantage of winter rains to cross the deserts on the trail and would arrive in California in early February. The return party would usually leave California for New Mexico in early April to get over the trail before the water holes dried up and the melting snow raised the rivers too high. The return party often drove several hundred to a few thousand horses and mules. In addition, low-scale emigration from New Mexico to California used parts of the trail in the late 1830s.
The Spanish Trail use lapsed after the War with Mexico ended in 1848 and Colorado became part of the United States. There was no longer any need to link Santa Fe with Los Angeles by this difficult mule trail; other, wagon-friendly routes were opened. However, the mule and horse tracks of the Old Spanish Trail are an important part of legacy celebrated by the Tracks Across Borders.
Long before the Old Spanish Trail was established the area was explored by Spanish priests. The Dominguez-Escalante expedition travelled through the area in 1776. Led by two Franciscan priests, Atanasio Dominguez and Silvestre Velez de Escalante, their mission was to find an overland route from Santa Fe to their mission in Monterey on the California coast. With eight men, they travelled through many unexplored portions of the west, including western Colorado, Utah, and Northern Arizona. Along part of their journey, they were aided by indigenous guides of the Timpanogos tribe (Shoshone or Ute people). However, hardships encountered in the harsh and unforgiving land forced the expedition to turn back to Santa Fe before reaching California. The maps and documentation produced by the expedition aided future travelers and their roue eventually served as a template for the Old Spanish Trail.