This subsection consists mostly of an alluvial plain in Truckee Meadows and the Spanish Springs, Washoe, Carson, and Diamond Valleys.  The climate is temperate and semi-arid.  MLRA 26f.

Lithology and Stratigraphy.  Quaternary alluvium predominates in this subsection. Hot Springs Mountain in Carson Valley is Triassic and Jurassic volcanic and sedimentary rocks, and there are Mesozoic granitic rocks and Tertiary andesite and silicic tuffs on Huffaker Hills, Prison Hill, Steamboat Hills, and on the divide between Carson and Washoe Valleys.

Geomorphology.   This subsection is predominantly on gently to moderately sloping alluvial fans and pediments and nearly level floodplain, terraces, and basin floor.  There are outwash fans at the foot of Mt. Rose and pediments on glacial outwash along the Truckee River.  Moderately steep to steep hills are prominent but only small parts of the subsection.  The elevation range is from 4400 to about 6000 feet.  Fluvial erosion and deposition and freeze-thaw are the main geomorphic processes.

Soils.  The soils are mostly Typic Torriorthents, Aridic Haploxerolls, and Xerollic and Durixerollic Haplargids on alluvial fans and pediments; Typic and Aquentic Haploxerolls and Typic Haplaquolls on floodplains and basin floors; and Aridic Lithic Haploxerolls, Aridic Haploxerolls, and Xerollic Haplargids on hills.  They are Entic Xerumbrepts and Haploxerolls on younger and Aridic Argixerolls on older outwash fans at the foot of Mt. Rose.  The soils are well to poorly drained.  Soil temperature regimes are mesic.  Soil moisture regimes are mostly aridic, and some xeric (nearly aridic), plus wet soils in basin-fill that have aquic moisture regimes.

Vegetation.   The predominant natural plant communities are Big sagebrush series on alluvial fans and Sedge meadow alliances on basin floors and floodplains.  Low sagebrush series is common on shallow soils in hills.  Jeffrey pine series occurs of some soils with xeric soil moisture regimes.

Characteristic series by lifeform include:

Grasslands: Alkali sacaton series, Ashy ryegrass series, Beaked sedge series, Creeping ryegrass series, Indian ricegrass series, Needle-and-thread series, Saltgrass series.

Shrublands: Big sagebrush series, Bitterbrush series, Low sagebrush series, Parry rabbitbrush  series, Rubber rabbitbush series, Tobacco brush series.

Forests and woodlands: Curlleaf mountain-mahogany series, Jeffrey pine series.

Surface Water.  Runoff is rapid from alluvial fans and slow from basin-fill.  Truckee Meadows and Spanish Springs Valley drain to the Truckee River, which flows from Lake Tahoe in the Sierra Nevada to Pyramid Lake in the Great Basin.   Diamond and Carson Valleys are drained by the Carson River, which flows to the Carson Sink.  Washoe Lake in Washoe Valley  has an ephemeral outlet to Steamboat Creek, which drains to the Truckee River.