Complex sentence: Several men were left behind as they dropped from exhaustion, but Pike doggedly pressed on until January 30, when he and the ten men who were still with him came to the Rio Grande at a point near Alamosa, Colorado.
Split into simpler sentences: Several men were left behind as they dropped from exhaustion, but Pike doggedly pressed on. By January 30, he and the ten men still with him came to the Rio Grande at a point near Alamosa, Colorado.