James R. Mills, a former Democratic legislator who led California’s senate during most of the 1970s and was credited with saving thousands of historic landmarks, has died. He was 93.

Mills died on March 27 after battling kidney cancer, his family members told the San Diego Union-Tribune.

During his 22 years representing San Diego in the state Assembly and Senate, the former middle school history teacher authored a law called the Mills Act to save historic buildings from being torn down by lowering property taxes for owners who preserve them. He also authored legislation that created San Diego’s 54-mile (87-kilometer) trolley system and Old Town State Park.

Mills also served as senate pro tempore from 1971 to 1980, the body’s top leadership position.

He introduced a constitutional amendment in 1966, later approved by voters, that made the Legislature a full-time operation.

Before then, lawmakers held a full legislative session every other year, with limited gatherings to pass a budget and deal with other pressing items in between.

The shift was intended to help the Legislature respond more quickly to the needs of a fast-growing state. But after it was implemented, Mills came to regret the changing, saying he felt that it robbed legislators of the time off necessary to reflect on what they were doing, and what they had done.

After he left the Legislature, Mills chaired the Metropolitan Transit Development Board in San Diego for nine years. Its headquarters is named after him. He also served stints on Amtrak’s board and the California High Speed Rail Authority.

“Dad believed that government existed to serve the people, and he fought for fairness, education, environmental protections, the coastline, the climate and public services,” his daughter Beatrice Germain said. “He was a real old-school progressive, and we are all proud of what he contributed.”

Besides Germain, Mills was survived by daughter Eleanor Howard, son Bill Mills and nine grandchildren.