You are looking for a bison tube, hanging at the posted coordinates.
Auston and I were walking along the trail today, and noticed there was room for a cache. The only container we had with us with this bright blue bison tube. Yup, it's really blue. It's now black.
Please bring your own pen to sign the log and replace as found. This can be a high muggle area, as it is close to the parking area for the trail. You may need to be stealthy.