No addtional info from above, but this photo is in the Library of Congress on it's website:
https://www.loc.gov/item/2017707945/
Title, date and keywords based on information provided by the photographer.
Credit line: John Margolies Roadside America photograph archive (1972-2008), Library of Congress, Prints and Photographs Division.
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However, Cinema Treasures has this information:
http://cinematreasures.org/theaters/61168/
XPO Adult Theater
3131 E. Anaheim St., Wilmington, CA 90734
This short-lived storefront adult cinema opened on July 4, 1973 and closed in 1974.
There is no photograph of the theater on the website or corroborating information, but would you describe the place in the photo as a "storefront adult cinema" and the '73-'74 date is also not 1977. Any clues here?
Looking at the GSV view of 3131 E. Anaheim St. now, it doesn't seem like this place would've been there, but the '70s were 50 or so years ago.