Two ways which might not be too difficult depending on the size of your area of interest:
Download from the USGS seamless server
1. a DOQQ or NIAP image (1 meter resolution) or
2. a NLCD (land classification) image (30 meter resolution) - fields, trees, water, etc are shown by different colors.
Either of these can be converted into a .kmz package and placed on the Oregon as a custom (image) map.
The lines, points and labels in the topo map will be drawn after the image map (polygons draw before and will be covered over).
There is a file size/coverage area limit to a custom map, so the DOQQ or NIAP imagery at 1 meter resolution (10,000 m by 10,000 m) may be too small for you purpose and you would also need some skill to interpert the imagery.
Lets us know if you decide to go this route and I/we can provide some additional help.