What was the main mountain pass wagon trains. Used by native Americans

The major southern routes were the Santa Fe Trail, the Southern Emigrant Trail, and the Old Spanish Trail, as well as its wagon road successor the Mormon Road, a southern spur of the California Trail used in the winter that also made use of the western half of the Old Spanish Trail.

Explanation:

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president thomas jefferson commissioned the expedition shortly after the louisiana purchase in 1803 to explore and to map the newly acquired territory, to find a practical route across the western half of the continent, and to establish an american presence in this territory before britain and other european powers