By Roberta Attanasio For six million years, the Colorado River ran from the Rocky Mountains to the Gulf of California—through 1,450 miles of mountains, deserts, canyons, and the lush delta in Mexico. Now, it no longer reaches the sea. The once vast and fertile delta of the river is dry—a parched wasteland. In 1931, the United States Bureau of Reclamation built the first of a series of large dams along the lower Colorado River, which now provides water to two states in Mexico and 30 million people in seven U.S. states. Until the 1950s, the delta was still a network of freshwater and marine wetlands with meandering river channels—an opulent habitat…