Many other springs do not seem to be controlled so strongly by faulting, but owe their presence to sources of volcanic or magmatic heat which exist near to the surface of the ground. Some springs of this type issue from Precambrian granite, or Cenozoic volcanic rock, while others flow from sedimentary rock layers. Waunita Hot Springs and Pagosa Springs, although near volcanic rocks, reach the surface through porous sandstones and shales of Cretaceous age. Mt. Princeton Hot Springs comes from alluvium but its heat source is the intrusive igneous rock which makes up part of the adjacent mountain. Springs of another general type are also present in Colorado where aquifers, generally sandstones, are dissected by erosion. These springs, usually not highly mineralized or warm, are most often found in the Plateau Province. Such springs are frequent at the bases of the great sandstone cliffs of Mesa Verde and Colorado National Monument. Manitou’s carbonated springs, which attract many tourists, have their origin in the arrangement and nature of the rocks through which the water flows. Water from the Pikes Peak region, slightly acid from its contact with the granitic rock, flows into the Manitou limestone all along Ute Pass fault, which extends from Cheyenne Mountain northwest to Woodland Park. Descending through channels along the fault, the water becomes pressurized. Because of its pressure and its acid content, it partly dissolves the calcium carbonate of the limestone, and from then on carries carbon dioxide in solution. As the water comes to the surface at the low point of the fault exposure, near the west edge of Manitou, the pressure is released and the carbon dioxide effervesces, just as a bottle of soda water effervesces when the cap is removed. ENVIRONMENTAL GEOLOGY The preceding part of this chapter mentions many ways in which man’s destiny in Colorado has been shaped by geologic factors. Early Coloradoans settled near gold and silver placers, later ones near mines that produced ores of other metals, or in the towns that sprang up around the mills and smelters that processed these ores. Our present distribution of population is partly a heritage from these first settlements, partly a result of later discoveries of oil, gas, and radioactive minerals, and partly a response to the state’s extreme topographic variation, which controls and delineates agricultural areas and transportation routes. In recent years, man has begun to appreciate the fact that he may benefit in other ways from knowledge about geology. A new geology has developed—_environmental geology_—which may be defined as the total of all geological conditions and influences affecting the life and development of man.