A final warning to the air traveler. He should be sure before deplaning that he has observed a _bajada_. It is a must. Bajada is one name, outwash slope is another, alluvial fan is still another. The stewardess should inquire of each student, and if his answer is “no,” she should reply, “Then you’ve just flunked the course.” A bajada is the most characteristic single feature of all in the sloping, stony topography of the desert—and remember that the surface of the desert is regularly sloping and stony. The Spanish word itself means only a down slope, but it has come to have a semitechnical sense—a fan-shaped apron of rocky debris at the foot of a mountain where it has settled out of the summer torrents and there keeps accumulating in successive floods. As the mass builds up, the bigger fragments drop out closest to the parent crag, then the small ones, finally the coarse gravel, and lowest of all on the slope the fine sand. Thus the fragments are graduated in size, in distance traveled, and in the nature of soil resulting. As the fan increases in size and laps up higher and higher on the mountain’s flank, the geologists often describe the result by saying that the mountain “is burying itself under its own debris.” From the air, the lines of drainage will be seen to have assumed the form of a tree with its trunk downward, its branches high in air. But the most interesting aspect of a bajada is the nice proportion which nature works out between the plant species and their location on the curve. FROM SAGEBRUSH TO SPRUCE TREES The traveler who has viewed the Southwestern panorama of nature from its sagebrush to its spruce trees has indeed seen most of it. The spruce which grows wild only well up on the higher mountains is familiar to everybody because it has become a favorite in formal planting everywhere. But the sages—who knows them? To the tenderfoot, almost any gray plant is “sage.” To my friends the cowmen, sage means commonly saltbush. To my friends the foresters, sage means an artemisia. But there are romantics to whom “purple sage” is Apache plume, which is a member of the wild rose family.