After the bombing of Pearl Harbor on December 7, 1941, many parts of the West Coast were declared military defense zones, and the government ordered the removal of all persons of Japanese ancestry. The War Relocation Authority, established in March 1942, placed them in inland camps, including the Heart Mountain Relocation Center, one of ten temporary camps built to confine more than 110,000 men, women, and children forced from their homes in California, Oregon, Washington, and part of Arizona. The only such camp in Wyoming, Heart Mountain began construction in June 1942, received its first internees in August, and at its peak held nearly 11,000 people in 450 barracks across more than 740 acres. Though enclosed by barbed wire and armed guards, the internees kept it operating as a small city with public works, grade schools, a high school, a hospital, and a newspaper, making it at the time the third largest city in Wyoming. The camp closed in November 1945, its buildings were removed, and land made arable by irrigation ditches completed by the internees was opened for homesteading. In August 1944, internees erected an Honor Roll there to honor people from the camp who served in the United States armed forces in World War II. Preserved in 1978, it remained to recognize both those Japanese-Americans who served in the military and the sacrifices of those interned there during the war, and in 1985 a plaque was erected for people from Heart Mountain who gave their lives in World War II.