The geologic map of the Fairfield 30′ x 60′ quadrangle identifies rock units exposed at the surface or underlying thin surficial cover of soil and colluvium.

Alluvial-fan deposits (Holocene and Pleistocene)—Moderate- to well-sorted, stratified, sandy pebble-cobble gravel grading southward to pebbly coarse sand and coarse sand. Forms large coalesced alluvial fan that emanates from the mountain front about 6 km (4 mi) north of Fairfield.

Alluvial fan deposits (Holocene) - Alluvial fan sediment deposited by streams emanating from mountain drainages onto alluvial valleys; composed of moderately to poorly sorted sand, gravel, silt and clay.

Quaternary basalts and gravels are wide-spread on the South Fork of the Boise River, and alluvial depos-its are common along active drainages. Metasedimentary rocks of unknown age crop out on House Mountain, Chimney Peak, and on the ridges east of Anderson Ranch Reservoir.

2025年1月10日 · Alluvial fans occur in areas with significant topographic relief caused by rapid subsidence or uplift (rift basins, foreland basins, fold-and-thrust belts, etc.). They are semi-circular in map view, form mounds in transverse cross section, and form basinward-thinning wedges in lateral cross sections.

The principal aquifers are sand and gravel in the alluvial fill, and basalt. Water in the shallow deposits is not confined, and the water table generally is less than 10 feet below the surface at most places.

Alluvium (from Latin alluvius, from alluere 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings.

The Fairfield series consists of very deep, well drained soils that formed in glacial outwash, alluvium, colluvium and till. These soils are on alluvial fans, fan remnants, stream terraces, till plains, and moraines.

An alluvial river is one in which the bed and banks are made up of mobile sediment and/or soil. Alluvial rivers are self-formed, meaning that their channels are shaped by the magnitude and frequency of the floods that they experience, and the ability of these floods to erode, deposit, and transport sediment.

The alluvial deposits are characterized by variation between more silty and sandy units (u20, u40, u60, u80, u100) and more clayey organic units having varying degrees of soil development (u30, u50, u70, u90).