of eruptions since the Miocene. The ages of the first eruptions are difficult to determine, since the older rocks have been almost entirely buried by the material from younger eruptions. The oldest exposed volcanic rocks in the vicinity are approximately 16 million years old. The Jemez area experienced an intense pulse of basalt volcanism between 9 and 11 million years ago. The lavas from this cycle had little silica, and originated in the mantle. Additional pulses of volcanism occurred between 7-10 million years ago, between 6-7 million years ago, between 3-6 million years ago, and between 2-3 million years ago. The last of these pulses is believed to have created the Cerros del Rio volcanic field, which covers the entire Caja del Rio Plateau. Climate The climate of the Caja del Rio is arid and continental. The average daily maximum temperature at White Rock, New Mexico varies from 39.7 degrees Fahrenheit in January to 80.5 degrees in July. The average daily minimum temperature varies from 18.8 degrees in January to 54.4 degrees in July. That average annual maximum temperature is 60.0 degrees, with the average annual minimum at 35.8. The average annual precipitation is approximately 10-12 inches. Most of the annual precipitation is associated with summer thunderstorms, although the area also receives winter snow. Ecology Soils in the Caja del Rio are derived from Tertiary volcanic basalt flows and cinder cone eruptions. Most are best characterized as stony or cindery loam, with shallow horizons. Soil surveys of the Caja generally describe the soils as unsatisfactory, with a reduced potential for hydrologic and nutrient function. Three primary plant communities are frequently found on the Caja del Rio plateau: pinon-juniper savanna, pinon-juniper woodland, and Great Basin sage scrub. The most prevalent vegetative communities consist of a pinon (Pinus edulis) and juniper (Juniperus monosperma) overstory with a short grass understory. Tree densities often range between 100 and 300 trees per acre. Another large community consists of open grassland, with blue grama (Bouteloua gracilis), galleta (Pleuraphis jamesii), and various species of Stipa being the most common grasses. Common woody shrubs include chamisa (Chrysothamnus nauseosus), Apache plume (Fallugia paradoxa), four-wing saltbush (Atriplex canescens), and big sagebrush (Artemisia tridentata). Predatory mammals known to live in the Caja del Rio include black bear (Ursus americanus), mountain lion (Felis concolor), bobcat (Lynx rufus), coyote (Canis latrans), fox (Vulpes spp.), gray fox (Urocyon cinereoargenteus), ringtail (Bassariscus astutus), badger (Taxidea