This letter box is a small plastic jar tucked down low! Arrive at the parking coordinates, and then exit your vehicle. Walk towards the waypoint sign until you are stopped by a man-made structure. Then lean down and check all the low places. This cache fits perfectly in its little spot, but should be visible by its green lid or brown bottom at the right angle. The stamp is on a magnet in the lid. You should be able to pull the magnet from the bottom of the lid so that you can stamp wherever you need to. The remaining magnets are stuck to the lid, but ended up not being needed for this hide style.
This cache is wheelchair accessible, provided your chair can navigate loose gravel over a hard-packed road/parking lot. It is located down low, so you will need to lean in your chair to access it, but it should be visible and accessible when seated.