Just west of South Fork, the Rio Grande forms a passage between the rugged San Juan Mountains and the open floor of the San Luis Valley, linking neighboring landscapes and cultures that together reflect a microcosm of Colorado’s past. The San Juan country, long an impregnable Ute stronghold, was transformed after 1880 by mining, railroading, and town building, while the San Luis Valley gave rise to modern Colorado’s first settlements and remains rooted in centuries-old Hispano traditions. In Colorado, the river runs clear and cold through a 180-mile course, though farther south in the United States it is known for carrying heavy sediment. From the snowmelt of the San Juan Mountains, the Rio Grande continues 1,900 miles to the Gulf of Mexico. Over generations, Utes lived from its fish and game, mountain men and fortune hunters followed its banks in search of furs, gold, and timber, and the Denver & Rio Grande Railroad used it as an important transit corridor. Above all, the river has been a catalyst for agriculture: farmers in New Mexico have drawn on it for thousands of years, Hispano pioneers in Colorado’s San Luis Valley tapped it as early as the 1840s, and today its waters irrigate fields from South Fork to the Gulf of Mexico, making it one of the world’s most heavily used irrigation resources.