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Drought in the Great Basin must be separated into at least two types: hydrologic or surface water drought and soil moisture drought during the spring to early summer growing season. Hydrologic drought typically occurs when snow pack is low and/or diminishes before the typical spring runoff period. Soil moisture drought affects vegetation growth, not surface flow, and is primarily a function of inadequate or poorly distributed precipitation during the spring growing season. Insufficient moisture in the root zone, in the spring, when soil and air temperatures are warm enough to support plant growth, results in decreased forage production, much more than total precipitation during the dormant winter season. Perennial herbaceous forage plants typically have 80% or more of their root biomass in the top 16 to 20 inches (41 to 61-cm) of the soil, and as much as 60% in the soil's top 8 inches (20-cm), where most nutrients needed for growth occurs. The water holding capacity of the soil layers inhabited by most of the root biomass is less, and sometimes much less, than the mean precipitation during both the dormant winter months (October-March) and the spring (April-June) growing season. Depending upon the size and frequency of discrete precipitation events once growth begins, the root zone can often be refilled with soil moisture when precipitation is less than average. This includes water years that are classified as moderate to severe drought. Photo documentation of plants in areas of northern Nevada classified as extreme or exceptional drought show that little if any adverse effect of the drought on plant growth and health. This can be explained, at least in part, by the amount and timing of precipitation and the soil's water holding capacity, with respect to the location of most of the root biomass of the forage plants.