These formations are stacked on top of each other and are separated by impermeable shales and siltstones. Main recharge areas are also along the southern and eastern peripheral belt. The local aquifers include alluvial deposits, which occur in washes and stream channels throughout the basin, sedimentary and volcanic rocks of the Bidahochi Formation, and various sandstones. Water enters the alluvium as discharge from the D, N, and C-aquifers, as streamflow infiltration, or as direct rainfall. In thicker sections the alluvium is a steady source of water, but smaller washes can go dry because of overuse or drought conditions.
Water quality varies greatly in the alluvial aquifers.
Radiochemical contamination is present in the alluvial aquifer along the Puerco River. The basaltic rocks form an irregular, eroded surface and vary in thickness from 0 to 3,000 feet. Groundwater is found in fractures, cinder beds, and heavily weathered zones. In the southeastern part of Navajo County, the saturated basaltic rocks, together with underlying sedimentary rocks, locally are known as the Lakeside-Pinetop aquifer. The Bidahochi Formation is composed of sedimentary and volcanic rocks.