We sure were challenged in finding information about Walla Walla, SE Washington and NE Oregon hiking trails. There is some information on the Umatilla National Forest website, but we later found out it was wrong in parts. We looked for an outdoors store in Walla Walla so we could buy a topographical map or a book on trails, and surprisingly, there is no such store in Walla Walla. We finally found a trailhead in the mountains but the the signs were blank slates with no information at all. I'm afraid the Umatilla National Forest has no budget for improvement of its hiking trails.
Best bet is to go on the Umatilla National Forest website and print out the information on the trails. A lot of it will be wrong or tough to follow. It gave directions on Forest Services roads, which were either nonexistent or we had no idea if you found the right road. Trailhead names weren't accurate. But you should at least find a trailhead with your printout and a good road map.
Walla Walla gets hot and dry in the summer and all the wild grasses turn yellow or brown. Two days before we arrived, Walla Walla was hit with a thunderstorm and the lightning ignited four wildfires in the area. One was still raging when we arrived, so unfortunately, the air was a bit smoky. Be careful with all those inflammables!