IN THE 1860s and 1870s several great surveying expeditions mapped the Rocky Mountain West. Accompanying the survey parties were photographers whose romantic images of the region's stupendous natural wonders awed the stay-at-home folks back east. The most famous of these photographers was William Henry Jackson -- his celebrated portrait of the Mountain of the Holy Cross in central Colorado has become the icon of the heroic age of western reconnaissance. But there were other photographers -- among them, Timothy O'Sullivan, John Hillers, Andrew J. Russell, and Alexander Gardner -- whose beautiful images are now the prized ornaments of various public and private collections. In 1977 the authors of this book hit upon the happy idea of rephotographing the peaks, passes, unusual rock formations, mining towns, and lakes that had been the subjects of the earlier pictures. The project took them on a three-year, 30,000-mile journey through the West and involved much lugging of equipment up and down mountainsides seeking the same vantage from which, say, Jackson had photographed a view. Here then are the results: 120 pairs of photographs, with the members of each pair separated by a century of geological and environmental change. Finding the often subtle differences between the two views of the same location is a challenging and intriguing pursuit (only the mining towns have altered dramatically). In general, whether one can say that not much has changed in the last 100 years, or that there have indeed been profound changes, seems to be as much a philosophical question as one of fact. For instance, the rephotograph of the Mountain of the Holy Cross shows no change at all, even to the debris in a rockslide at the foot of the mountain, whereas in the rephotograph of Hanging Rock in Echo Canyon, Utah, (see above and below) the river has changed course and a large boulder called Pulpit Rock (from which Brigham Young once preached to the Mormon faithful) has disappeared as a result of roadbuilding; still, there is Hanging Rock in all its glory. The problem of change is but one aspect of this curious and fascinating book.