The high, rugged Carson Range and Sierra Nevada mountains on the eastern California border were the final obstacles that had to be overcome before westbound travelers could proceed. The Sierra Nevada comprise a large block of weather-worn granite tilted towards the west. They extend about from near the Fandango Pass in the north to the Tehachapi Pass in the south. The western slopes are scarred by glacier and river carved canyons but slope much more gradually west taking about to fall from their rugged over crests to the about elevation of the Central Valley. The even more rugged glacier and river scarred eastern slopes are typically much more precipitous, rising to the rugged Sierra crest from their about base in the Great Basin in many places in less than .