1. Average topography, isostatic residual gravity, and aeromagnetic maps of the Parkfield Region, California [microform] Yale Public content 1989. 2002-06-01T04:00:00Z. 2002-06-01T04:00:00Z. Geological Survey (U.S.). Department of the Interior, Survey ; Books and Open-File Reports Section, distributor. English. Public. California and Parkfield Region.