Two WPA parks that I have been two are Civic Stadium in Eugene, Oregon
http://www.ballparkreviews.com/eugene/eugene.htm#
and Olympic Stadium in Hoquiam, Washington.
http://www.ballparkreviews.com/hoquiam/hoquiam.htm#
Both ballparks were featured in David Eskenazi's photo essay in the
2006 SABR publication "Rain Check".
Mark