In the House, Miller was a member of the Natural Resources Committee; he was that Committee's chairman from 1991 to 1994. Miller supported efforts to preserve public lands such as the 1994 California Desert Protection Act, which among other things created Death Valley National Park and Joshua Tree National Park. In addition, Miller was the chief sponsor of the Central Valley Project Improvement Act of 1992, which mandated that the federal government's Bureau of Reclamation manage the Central Valley Project in order to better protect the fish and wildlife populations of California's Bay-Delta region. Miller lost his chairmanship when Republicans won control of Congress in 1994. He stayed as the committee's Ranking Member until 2000. and remained on the committee as a member until 2015. Miller was also a member of the Congressional Wildlife Refuge Caucus.