The city was on historic U.S. Route 66 in California, present-day Colorado Boulevard, with businesses serving travelers on it.

Santa Anita Assembly Center

In 1942 during World War II, Arcadia's Santa Anita Park racetrack became the site of the Santa Anita Assembly Center for Japanese AmericanU.S. citizens, where they were processed, after being removed from their homes and communities for forced relocation and internment under President Franklin Roosevelt's Executive Order 9066. The Civilian Assembly Center at the racetrack became the largest and longest operating one of the eighteen, all were holding citizens until the Relocation Center camps were completed in interior areas of California and other states.[26] More than 18,000 persons resided at the racetrack in primitive conditions.[26][27] 400 temporary tarpaper barracks were constructed on the racetrack grounds to housemany of the prisoners, where they lived three families per unit. 8,500 prisoners lived in converted horse stalls.[26] Bachelors were housed in the grandstand building.[26] They took group showers, lacked private bathrooms, and were under 24-hour armed surveillance. Conditions were extremely difficult, with each resident being given an “Army manufacture bed, one blanket and one straw tick.”[28] The Assembly Center held people from late March through the end of October 1942, when the internees were relocated inland to permanent internment camps at Manzanar and Tule Lake in California, and eight others in Western states and Arkansas.

At the time, Arcadia's civic leaders were very vocal in their support of the Japanese American relocation internment policies of the federal government. The Santa Anita Assembly Center site is California Historical Landmark