It is very difficult (at least for me) to determine the exact species of the wild roses because there are several and the differences are very slight, but I think believe is rosa woodsii. It is growing at the border of a dense thicket of Black Hawthorn in a very large, open prairie.
Near the start of the trail, where it first crosses the stream, the vegetation is heavy at the crossing. The flowering shrub to the right of the trail is called “Ocean Spray”.
Ocean-spray, Creambush ~ Holodiscus discolor
Sometimes a tree will fall across the trail. This one is a couple miles up from the trail head. For perspective, I leaned my hiking staff on the tree: the staff is 62 inches long.
Brown-eyed Susan ~ Gaillardia aristata
White Spirea, Shinyleaf Spirea ~ Spiraea lucida
Many flowers have already completed their summer and have already gone to seed. This one is from a Yellow Salsify.
I think this one is from a species of Butterweed.
Common St. Johnswort, Klamath weed ~ Hypericum perforatum