You may also like walking up the Lamar River beginning from where Soda Butte Creek flows into the river. That's a little bit less of a fishing mecca than Slough Creek, so you might see fewer hikers, if you care about that.
You can do day hikes in the Lamar Valley or up in the Soda Butte Creek valley also. It's enjoyable walking in those areas and I've seen wolves and bears as well as lots of bison and elk, of course.
If you do hike Slough Creek, after you get over the hill and drop into the first meadow, make sure you go over and have a look at the creek up close, I think you'll like seeing all the fish there even if you aren't a fisherman. There's another big meadow a few miles above the first one, but going to the second meadow would be a long day hike.