The Los Angeles County Fairgrounds was selected as one of the Southern California detention camps.

[1] Construction on the Pomona Assembly Center began on March 21, 1942, and the camp officially opened on May 7, 1942.

Large venues that could be sealed off were used, such as fairgrounds, horse racing tracks and Works Progress Administration labor camps.

These temporary detention facilities held Japanese Americans while permanent concentration camps were built in more isolated areas.

The order required all native-born Americans and long-time legal residents of Japanese ancestry living in California to surrender themselves for detention.

The depot stored vast supplies needed for the Desert Training Centers in California and Arizona.

For World War II the camp housed 500 German POWs starting in October 1944.

In May 1945 fire started at the camp depot, gas bombs, hand grenades, and small arms ammunition exploded.