The William Wrigley Jr. Summer Cottage, or "Mount Ada", is a historic residence located at 76 Wrigley Road in Avalon, on Santa Catalina Island, California.

The house was built in 1919–1921 as a summer retreat for the Wrigleys of Chicago, who owned 99% of Santa Catalina Island, one of the Channel Islands of California.

[3] In its heyday, the Wrigleys entertained Presidents Calvin Coolidge and Warren Harding, and the Prince of Wales at the house.

[3] In the 1970s, it was donated to the University of Southern California, and it was used as a conference center.

This article about a property in Los Angeles County, California on the National Register of Historic Places is a stub.