Lava Beds National Monument is on the Modoc Plateau in Modoc and Siskiyou Counties. The principal geologic units in the vicinity are volcanic rocks, which in places are highly permeable and poorly permeable lake sedimentary deposits, all probably post-Oligocene in age. Yields and specific capacities of wells in the unconfined water body within volcanic rocks and lake deposits range widely, but in general are low in the lake deposits and higher in the volcanic rocks. A confined water body occurring in volcanic rocks underlying the lake deposits yields large quantities of water to three wells in the study area.
Dissolved-solids content of ground water generally increases in proportion to the thickness of lake deposits penetrated and to proximity of the lake deposits. Water from wells drilled in the volcanic rocks several miles from the lake deposits and from wells penetrating the confined water body in volcanic rocks underlying the lake deposits contains small to moderate quantities of dissolved solids.
Ground-water supplies can be developed almost anywhere in the study area by drilling wells to depths below the water table. In addition, there is a reasonable possibility of developing wells in a confined water body underlying the water-table system.