Big Sage ReservoirBig Sage Reservoir is an artificial lake in Modoc County, California and Modoc National Forest. Its waters are impounded by Big Sage Dam, which was completed in.HydrologyThe lake discharges into Rattlesnake Creek, a tributary of the Pit River.Big Sage DamBig Sage Dam is an earthen dam long and high, with of freeboard. Hot Springs Valley Irrigation District owns the dam.RecreationFacilities include a campground and boat ramp, both located just north of the dam.