Thus, from here it is a short step to the realization that a number of geologic processes and agents working over long periods of time have given rise to innumerable features and structures ranging from the loftiest mountains down to the smallest hills and valleys; from the soil which grows our food to the gasoline and coal which feed our industries; from our huge iron ore deposits down to the much smaller, but now no less significant, deposits of uranium. How is all this related to a national park? Nowhere within our land can the accomplishments of the great geological processes, or their present-day operation, be seen to better advantage than in many of our national parks and monuments. In fact, it is for this reason principally that many of them were established. Notable is Grand Canyon National Park, containing the most spectacular part of the Colorado’s mile-deep canyon cut during the past million or so years through a series of rocks which themselves record a billion or more years of Earth history. Mount Rainier is the largest volcano in the United States. On it glaciers are now wearing away materials formerly extruded and piled up to spectacular height by volcanic forces. Crater Lake lies in the sunken throat of a volcano which at one time probably rivaled Rainier in size. In Carlsbad Caverns and Mammoth Cave National Parks are two of the world’s largest caverns which clearly demonstrate the tremendous effectiveness of subsurface water in dissolving limestone. Bryce Canyon and Zion National Parks and the Badlands National Monument illustrated on a much smaller but no less spectacular scale than the Grand Canyon the wonderful erosive power of running water. In Grand Teton one can see a huge block of the crust which has been raised thousands of feet along a high-angle fault, and at Lassen Peak in California and Craters of the Moon in Idaho there are exhibited some of the most recent volcanic features north of the Rio Grande. Despite Yellowstone’s wildlife and fishing it is best known perhaps for its geysers. This brief list is by no means complete, for something of prime geologic interest can be found in almost every national park and monument.