Though the Great Southwest is now the most sparsely inhabited region of its size in the United States, it was once the most populous and wealthy, probably more populous than it is to-day, with all its present American enterprise. Hundreds of years before the Spaniards first appeared in the New World, the valleys of Arizona and New Mexico contained a numerous population, supporting considerable cities, and irrigating extensive tracts of land with wonderful engineering skill. Frank H. Cushing, the anthropologist, who in 1882-83 wrote of the ruins of the Southwest, estimated that the irrigated valleys of Arizona were once the dwelling-place of two hundred and fifty thousand people, about twice the population of the entire Territory then. The remains of these ancient civilizations--the pueblo-dwellers, the cliff-and cave-dwellers--are found scattered everywhere throughout Arizona and New Mexico, and in such numbers that archæologists have only begun to explore them. No part of the United States, indeed, has had a more thrilling and eventful history. While denominated a desert "not worth good blood,"--in the words of the historian,--it has been a center of contention for centuries, overwhelmed by one tide of conquest after another. From the time that the Spaniards first invaded the country, hunting for gold, down to the capture of Geronimo by American soldiers in the eighties, it has been the scene of many bloody Indian wars. It was the source of contention between the United States and Mexico in the war of 1846-48. Once a possession of Spain, and later of Mexico, the story of the struggle for independence by the Texans and for annexation by the Californians is full of fascinating interest. Its soil has developed some of the boldest and most picturesque characters in American history--Boone, Crockett, Kit Carson, Sam Houston, and many a pioneer cattleman and settler, to say nothing of the Crooks and the Lawtons of the Indian wars. The main trail of the El Dorado hunters of '49 on their way to California let through it, garnishing its history with many a story of bloodshed and hardship. No American fiction is more vital and characteristic than that which deals with the early lawless days of the miner, the buffalo-hunter, and the cow-boy; none is more richly colored, picturesque, or rudely powerful. [Illustration: Mummy cave, Cañon del Muerto, Arizona.]