The Agua Mansa Valley is located on the south side of Slover Mountain. The valley was in length; its width varied between and , the variance depending on the river that flowed through the valley. The area was used as farmland, divided into at least one hundred fields, owned by separate farmers. The valley's lower end included a Frémont's cottonwoods (Populus fremontii) riparian forest owned by Rubidoux, while the upper end was a sandy plain that extended to the borders of present-day San Bernardino.