Just a quick report - I tried out the Summitview Trailhead of the Cowiche Canyon trail system. It is about 5 miles west of Yakima, just before you get to the top of the hill. Watch for it on the right - it's easy to pass right by (see pictures).
I did the Radio Flyer Loop, then jumped on the Summitview South Loop on the way back. I think total 3-3.5 miles, around 90 minutes.
Trails were muddy in places due to the rain, but small flowers starting to appear - purples and yellows. Just a beautiful place to be, even on a rainy day.
These trails are great for walkers, trail runners and kids - it's relatively flat once you get up to the main trails. Boots were helpful (due to the mud), I didn't even use my poles.
These trails are NOT good for people looking to escape humanity - I didn't see anyone, but you see signs of people all along the way. Houses, fences, and along part of the Radio Flyer Loop, you wander near a big garbage heap. I pretended it was an anthropological site, that seemed to help.
Also probably NOT good on a July afternoon. Perfect on a cloudy March one like today, but very little shade, so you would bake in the summer. But trails are nice and wide - good if you are afraid of snakes in the summer. None of that "wading through tall grass" business.
Trails were well marked, but it was handy to have a map in my pocket. Here's a link if you want to print your own:
http://www.cowichecanyon.org/docs/Uplands%20Map%20COLOR%202016%20new.pdf
All in all, a great escape - just what I needed as I face my 7th graders the week before Spring Break!