level. Over the years, many of these underground spaces have been filled or destroyed by subsequent development. However, it is still possible to view portions of the "Sacramento Underground". Modern era The city's current charter was adopted by voters in 1920. As a charter city, Sacramento is exempt from many laws and regulations passed by the state legislature. The city has expanded continuously over the years. The 1964 merger of the City of North Sacramento with Sacramento substantially increased its population, and large annexations of the Natomas area eventually led to significant population growth throughout the 1970s, 1980s, and 1990s. Sacramento County (along with a portion of adjacent Placer County) is served by a customer-owned electric utility, the Sacramento Municipal Utility District (SMUD). Sacramento voters approved the creation of SMUD in 1923. In April 1946, after 12 years of litigation, a judge ordered Pacific Gas & Electric to transfer the title of Sacramento's electric distribution system to SMUD. Today SMUD is the sixth-largest public electric utility in the U.S. and is a leader in innovative programs and services, including the development of clean fuel resources, such as solar power. The year following the creation of SMUD, 1924, brought several events in Sacramento: Standard Oil executive Verne McGeorge established McGeorge School of Law, American department store Weinstock & Lubin opened a new store at 12th and K street, the US$2 million Senator Hotel was opened, Sacramento's drinking water became filtered and treated drinking water, and Sacramento boxer Georgie Lee fought Francisco Guilledo, a Filipino professional boxer known as Pancho Villa, at L Street Auditorium on March 21. Early in World War II, the Sacramento Assembly Center (also known as the Walerga Assembly Center) was established to house Japanese Americans forcibly "evacuated" from the West Coast under Executive Order 9066. The camp was one of fifteen temporary detention facilities where over 110,000 Japanese Americans, two-thirds of them U.S. citizens, were held while construction on the more permanent War Relocation Authority camps was completed. The assembly center was built on the site of a former migrant labor camp, and inmates began arriving from Sacramento and San Joaquin Counties on May 6, 1942. It closed after only 52 days, on June 26, and the population of 4,739 was transferred to the Tule Lake concentration camp. The site was then turned over to the Army Signal Corps and dedicated as Camp Kohler. After the war