It was during this period San Francisco built some of its most important infrastructure. Civil Engineer Michael O'Shaughnessy was hired by San Francisco Mayor James Rolph as chief engineer for the city in September 1912 to supervise the construction of the Twin Peaks Reservoir, the Stockton Street Tunnel, the Twin Peaks Tunnel, the San Francisco Municipal Railway, the Auxiliary Water Supply System, and new sewers. San Francisco's streetcar system, of which the J, K, L, M, and N lines survive today, was pushed to completion by O'Shaughnessy between 1915 and 1927. It was the O'Shaughnessy Dam, Hetch Hetchy Reservoir, and Hetch Hetchy Aqueduct that would have the largest effect on San Francisco. An abundant water supply enabled San Francisco to develop into the city it has become today.