Free California GIS Data Sources

California Spatial Information Library (CASIL) provides the State GIS data of the State of California. If you browse through the site, you will find imagery - Digital Orthophoto Quadrangle GeoTiff (DOQQ), SPOT imagery and much more.

For California Landsat 7 imagery data products you can access these data, here.

Here's another link if you need 7.5 minute Digital Elevation Models for California
1:24,000-scale quadrangles.

For Digital Orthophoto Quadrangle (DOQs) and other imagery data products, these data are available directly from this link.

The California Digital Conservation Atlas is a comprehensive public website for conservation information.

You may want to check also the California Vegetation Map Catalog. This catalog allows you to find a variety of vegetation map data sets that cover the entire state or specific parts of the state, with an emphasis on county-level or larger data sets.