Rising From the Plains by John McPhee (Farrar, Straus & Giroux $15.95; 214 pp.)

California was not the last American frontier. A full half century after the lure of gold brought settlers to these shores, the frontier shifted eastward, back to those empty spaces of the High Plains that were passed over in the rush to the coast. In “Rising From the Plains,” John McPhee gives us a glimpse of this open, sparsely settled land--its geology, the story of some of the people who settled it, and some rather disturbing thoughts about its future.

He uses a device that he has used successfully before, both in his articles in the New Yorker and in books like “Basin and Range.” He attaches himself to a geologist and roams around the countryside, seeing what is there through the eyes of an expert. In this case, he was particularly lucky in his choice of traveling companion, for David Love of the U.S. Geological Survey in Laramie, Wyo., not only made a lifetime’s experience available to McPhee, but also the unpublished diary of his mother, who came to Wyoming on a stagecoach near the turn of the century.

The Rocky Mountains are probably one of the hardest mountain ranges in the world for geologists to understand. They are a complex structure and have a correspondingly complex history. If we want to understand the land we see, whether we are glancing casually from a car window or tackling the terrain with a geologist’s hammer, we have to understand all the events that have shaped it. Every bed of rock, every outcropping, has its story to tell about some era in the distant past. I know of no author who is better able to give us a feeling for the land we live on than McPhee.

He begins each narration with a trip that he took with Love. Sometimes the locale is accessible to everyone--a cruise along Interstate 80 in Wyoming, for example. Sometimes the trip involves going far from maintained roads in a four-wheel-drive vehicle. The end product of each trip is always the same. Starting with a given rock or hill, he leads us into the fascinating world of the geologist--a world in which seemingly permanent features of the landscape such as mountains or oceans change and evolve over unimaginably long periods of time. We see the Rockies forming as vast blocks of old rock are shoved laterally across the tops of their younger neighbors. We see a period when the Rockies were buried almost to their peaks in sediment and volcanic ash, then another period when the entire region was lifted up, allowing weathering to clean off the soft over-layer and give the mountains their present appearance. (McPhee calls this process “rising from the Plains,” which explains his title.)

Sometimes the simplest observation leads to the most profound insights. We all learned in school, for example, that Wyoming is a state with straight boundaries--one of two squares in the map of America. I always thought this in some way unnatural--there are, after all, no straight lines in nature. McPhee points out, however, that the rivers we normally think of as natural dividing lines on the map are also ephemeral when viewed against the grand backdrop of geological time. Even the oldest river in the United States (called, oddly enough, the New River) is much younger than the Appalachian mountains through which it flows. Lines, rivers--to a geologist one is as temporary as the other.

One word of warning is in order here. In discussing the Rockies, McPhee uses geological terms without embarrassment or apology. This shouldn’t be a problem--terms like paleozoic and cretaceous carry no more intrinsic difficulty than does a term like medieval . You might want to keep a dictionary at your side if this bothers you, but you will definitely find that the book will repay this small effort.

When he turns from the land of the West to its people, McPhee relies heavily on the diary of Ethel Love (nee Waxman), a Phi Beta Kappa graduate of Wellesley who came to Wyoming as a schoolteacher, married John Love, a local rancher, and, in the manner of Western women, shared in the building of one of the largest ranches in central Wyoming. It gives an unromanticized, accurate picture of what it was like to try to tear a living out of the arid grasslands in an area where wind and winter conspire against you. What comes through is a feeling for the resiliency--the sheer toughness--of the people who settled and still live in that open country. Everyone will come away with a favorite story from this part of the book. My own concerned an incident during the Great Depression when the banker came to foreclose on John Love’s livestock. After hearing the news, Love courteously asked his guest to step outside so that he (Love) could curse him. As a traditional Westerner, he wouldn’t dream of using such language under his own roof. (The banker complied with the request, then took the livestock.)

The most disturbing part of the book is also the shortest--some thoughts at the end on the future of the beautiful land that makes up so much of the West. The mineral resources of this region are great--there is more petroleum in the oil shales of western Wyoming, for example, than there is in Saudi Arabia. Even the crown jewel of the National Park System--Yellowstone--may contain exploitable resources. Will it be written to our everlasting shame that where weather failed our greed succeeded? That we destroyed both land and people where the mountains stand, rising from the plains?