More recently, as the railroads have spanned the continent at different points, we have knowledge of several deserts. There are the "Nevada Desert," the "Black Rock Desert," the "Smoke Creek Desert," the "Painted Desert," the "Mojave Desert," the "Colorado Desert," etc.; the "Great American Desert" being the name now applied to that alkali waste west of Salt Lake in Utah. As a matter of fact, however, these are but local names for a great section of arid country in the United States from two hundred to five hundred miles wide, and seven hundred to eight hundred miles long, and extending far down into Mexico, unbroken save for an occasional oasis furnished by nature, or small areas made habitable by irrigation. Where the old Union Pacific drew its sinuous line across the northern section of the desert, a trail of green spots was left to mark the various watering-stations for the engines. The Southern Pacific railroad left a similar line of oases down through the Colorado Desert, and the Santa Fé, in like manner, dotted with green spots the Great Mojave Desert. The water at these stations is obtained in some instances by drilling wells, and where it can not be obtained in this manner it is hauled in tank cars from other points. [Illustration: THE DESERT From photograph by C. C. Pierce & Co.] A portion of the desert lies below the level of the sea. Death Valley, in the Great Mojave Desert, has a depression of one hundred and ten feet below sea-level, while portions of the Colorado Desert lie from a few feet to four hundred feet below ocean-level. In the latter desert there are 3900 square miles below sea-level, and there are several villages in this desert which would be many feet submerged were the mountain wall between sea and desert rent asunder. There is a mystery about the desert which is both fascinating and repellent. Its heat, its dearth of water and lack of vegetation, its seemingly endless waste of shifting sands, the air of desolation and death which hovers over it,--all these tend to warn one away, while the very mystery of the region, the uncertainty of what lies beyond the border of fertility, tempts one to risk its terrors for the sake of exploring its weird mysteries.