Complex sentence: The tribe also owns the Red Willow Production Company, which began as a natural gas production company on the reservation, but has expanded to explore for and produce oil and natural gas in Colorado, New Mexico, and Texas.
Split into simpler sentences: The tribe also owns the Red Willow Production Company, which began as a natural gas production company on the reservation. It has expanded to explore for and produce oil and natural gas in Colorado, New Mexico, and Texas.