From the KCET post:
"In 1826, American fur trapper and explorer Jedediah Smith blazed a trail from present-day Utah to the Mojave Desert. After a clash with hostile Mohave Indians, Smith met two Tongva guides who offered to take his expedition to Mission San Gabriel, near Los Angeles. The guides led Smith along the intermittent Mohave River and over the San Bernardino Mountains near the Cajon Pass. Smith's party arrived at the mission on November 27, where they were warmly received by the missionaries...
Three years later, Santa Fe merchant Antonio Armijo led the first successful caravan from Santa Fe to Southern California, combining Smith's route with portions of the Franciscans' 1776 path to Utah to open what would later be called the Old Spanish Trail. In doing so, Armijo had established an important link between California and New Mexico, now the northern flanks of the newly-independent Mexican Republic."
Read more at the blog.