I have hiked this trail many times and it's beautiful with about 7 Bridges intertwining between the two canyons. However, today on May 25th my roommate and I pulled up to three broken car windows that have been bashed in while people were on their hike. Be aware and beware!
This trail system is about 5 miles from my house, and we've been there several times. It can be easily done on a hybrid bike, and is a blast on a mountain bike. The trails up to the rim are great for exploring and the area is a lovely little bit of nature close to Yakima.
If you live nearby or are visiting Yakima and want a short hike, this is a great option. If you're travelling, there are more worth-while trails a little to the west up White or Chinook Pass.
Hiking is just has fun. I listed the activity as mountain biking just because there aren't very many of those on this site.
Cowiche Canyon offers a lot of hiking bang for the buck. Because of its unique geological features each side of the canyon walls are different from the other.
One side of the canyon is basalt cliffs left from the Missoula Flood some 15,000 years ago while the other walls were upheaval if the earth. Regardless if which direction you hike on this 6-mile there and back trip, the scenery is different making it almost as if you'd gone elsewhere.
The trails are well groomed with few exceptions. Water from the stream is available to those with purifiers. Nearly a dozen bridges are available for stream crossing.
Since we went on a weekend, there were a lot of folks in this well used trail. However, it never truly was overcrowded.