Happy Valley AA was created in 1950.
Happy Valley Reservoir was created in 1897.
Happy Valley Beijing was created in 2006.
Happy Valley Shanghai was created in 2009.
Happy Valley-Goose Bay was created in 1941.
A Romance of Happy Valley was created on 1919-01-26.
If it is the name then it is proper and should be capitalized Happy Valley but if you are saying, I saw a happy valley as in the valley was happy then it is common.
Proyecto AA was created in 1991.
EMC AA was created in 1940.
Eastern AA was created in 1932.
AA Torque was created in 2005.
Toyota AA was created in 1936.
AA UU was created in 1986.