Likely your county's Extension Service office can direct you to a resource for that sort of info.

Locate that office with this interactive map:

http://npic.orst.edu/pest/countyext.htm

You don't say how much slope and how large is your garden but maybe try what has been for thousands of years in hilly farming, Terracing or in essence raised gardening that steps down the slope. JMHO Aloha