Santa Rita Experimental Range was founded in 1903. It is the longest continuously active rangeland research facility and among the five oldest biological field stations in the United States. The site is broken into distinct pastures, through which cattle graze throughout the year in various densities and durations. When the monsoon rains begin in early July, cattle are allowed to graze for approximately 10 days in a pasture before moving on, which prevents them from grazing plants a second time during the short summer growing season. Cattle grazing during the dormant season is also carefully managed. Climate:
Santa Rita Experimental Range receives 28-50 cm of rain per year, depending on elevation. Rainfall is bimodally distributed between winter storms originating in the Pacific Ocean and summer monsoonal moisture stemming from the Gulfs of Mexico and California. A majority of precipitation falls during intense, short duration summer thunderstorms. Dominant Vegetation:
The current vegetation at Santa Rita Experimental Range is a mix of short trees, shrubs, cacti and other succulents, perennial grasses, and other herbaceous species. Over the last 100 years, mesquite tree abundance has steadily increased across the range (McClaran 2003). Soil:
Three soil orders (Aridosols, Entisols, and Mollisols) consist of, or developed from, recent alluvial deposits.