Prairie Hill was once home to a ground-mounted L-4 cab built in 1933. It has been gone for many, many decades. Patrol engines still use this vantage point to look for fires.
Access is off Forest Road 16. The spur road is full of tire-piercing rocks so take it slow and you should be fine. Something with decent ground clearance would be helpful too, or walk from the pavement. This also appears to be a bit of a party spot so make sure the cache is well hidden.
You're looking for a small plastic container.