The United States Army Corps of Engineers built the zoned earth-and-rock-fill dam at the foot of the San Bernardino Mountains to protect against flooding in the eastern portion of the Greater Los Angeles Area. Its maximum height is above the pre-existing streambed and above the lowest portion of the foundation. The reservoir is medium-sized at , though it is a bit large for a reservoir whose sole purpose is flood control, which means that water is released as soon as safely possible, while still slow enough to allow water to seep into the streambed, recharging the groundwater aquifer. Also, releases are coordinated with Prado Dam, which is downstream.