The Apple Valley Kiwanis Wine Country Trek follows some nice side roads from Yakima to Prosser and back. Actually, the "back" portion is flatter and smoother than the "to" portion, but the "to" portion goes past several wineries (hic!).
I'd point at the map, but it looks like the Apple Valley Kiwanis website has been hacked. Here's a link to the Active.com registration page:
http://www.active.com/cycling/yakima...try-trek--2012