the Reserve was co-managed by both NPS and IDPR. After the approval of a comprehensive management plan, the NPS officially transferred on-site management of the Reserve to IDPR on May 2, 1996. Today, the park functions under a unique cooperative agreement between the NPS and IDPR. Both agencies allocate partial funding to its operation. City of Rocks National Reserve is visited annually by over 80,000 visitors. The Reserve headquarters is located in the gateway community of Almo. Environment City of Rocks, an extraordinary encirclement of granite rising out of the gently rolling sagebrush country in south-central Idaho, has attracted and intrigued people since they first entered this region. The Shoshone camped here as did the emigrants traveling along the California Trail. One of the reserve's most notable qualities is its large degree of biological diversity concentrated in a relatively small area. The great variety of textures, colors, and shapes in the natural landscape contributes considerably to the reserve's scenic quality. Geologic formations The landscape of City of Rocks has been sculpted from granite that was intruded into the crust during two widely spaced times. The granite that composes most of the spires is part of the 28-million-year-old Almo pluton. However, some of the spires are made of granite that is part of the 2.5 billion-year-old Green Creek Complex that contains some of the oldest rocks in the western United States. The granite has eroded into a fascinating assortment of shapes. City of Rocks was designated a National Reserve, a unit of the National Park Service, in recognition of the nationally significant geological and scenic values of its rock formations and the historical significance of the California Trail. Rock formations in the reserve developed through an erosion process called exfoliation, during which thin rock plates and scales sloughed off along joints in the rocks. The joints, or fractures, resulted from the contraction of the granite as it cooled, from an upward expansion of the granite as overlying materials were eroded away, and from regional tectonic stresses. The granite has eroded into a fascinating assortment of shapes as high as . The upper surfaces of many of the rocks are covered with flat-floored weathering pits known as panholes. The most notable panhole is located on top of Bath Rock and is continuously filled with water from rain or snowmelt. Animals Located in the Northern Basin and Range/Snake-Columbia shrub steppe ecoregions and the