Did not find a John Gamblin (soundex) in Riverside County on the 1920 however did find the following.
1920 California, Monteray County, Peachtree/San Lucas Township, ED#283, Page 276A, No Date:
John H. Gamblin, 42yo, MO KY MO, Farmer
Linnie S.?, wife, 34yo, MO MO MO, Teacher/Schoolroom
Esther M., daughter, 9yo, CA MO MO
John P., son, 7yo, CA MO MO
1930 California, Stanislaus County, Modesto City, ED#19, Page 213A, 4/10/1930:
John H. Gimblin, 50yo, M@25yo, CA MO KY, Truck Driver/Oil ?
1930 California, Riverside County, Riverside City, ED#37, Page 184A, 4/12/1930: (4566 Orange Street)
Minnie S., 43yo, widowed, MO MO MO, Teacher/Public School
Mary E., daughter, 19yo, CA MO MO
J. Paul, son, 17yo, CA MO MO
also living at same address....apartment?
Kenneth McKenzie, 68yo, Can Scot NovaScotia, 1883/Na, Broker/Real Estate
Luella, wife, 59yo, MI NY NY
again at same address.......
Lulu M. Biggers, 44yo, Divorced, MO KY MO, Saleslady/Real Estate
California Death Index (1940-1997)
John Paul Gamblin b. 12/13/1912 d. 3/31/1942 Riverside County, Mother's Maiden Name Schafer.S/S#568-20-2375