Bitter Spring was a water and food source for the Native American peoples that lived in this part of the desert. It became a watering and grazing place between Salt Spring and the Mojave River on the Old Spanish Trail. It passed 38.75 miles south through Silurian Valley, then east through the Avawatz Mountains at Red Pass and beyond the playa of Red Pass Lake, through a gap between the Soda and Tiefort Mountains to Bitter Spring in a wash in the next valley. From Bitter Spring the trail led 18.75 miles southwest climbing Alvord Mountain to cross Impassable Pass to descend Spanish Canyon and cross the plains to the location of Fork of the Road on the north side of the Mojave River where it met the Mohave Trail, that had become another branch of the Old Spanish Trail, often called the Main Branch that later became a wagon road called Government Road or Mojave Road.