Environmental Description:  This type occurs in the foothills of a small mountain range in a semi-arid region. This region is characterized by thrust faulting, with north/south-trending ranges and intervening broad, gentle valleys. The climate is semi-arid, averaging 50 cm (20 inches) of annual precipitation, with summer months receiving slightly less than the remainder of the year. Summers are warm and winters cold, but can occasionally be moderated by incursions of Pacific maritime air masses.

The association occurs on a gently sloping valley-side at approximately 1870 m (6140 feet) elevation. Formation Spring emanates from the base of the Aspen Range and flows across the valley floor for about 1 mile, where it then sinks into the porous substrate. The water of the spring is supersaturated with very pure calcium carbonate (CaCO2), and extensive deposits of travertine have precipitated out of solution along the course of the spring water. The water flow has been continuously changed by damming action resulting from the travertine deposition. This process has occurred over thousands of years and has resulted in many features, including active and inactive (dry) rimmed pools that have built up to a depth of 3.6 m (12 feet), and level, barren plains. No information is available on soils that have developed from these highly calcareous substrates. This plant association occurs away from the high water table along the creek, in the inactive, dry travertine pools.