Permission was granted by the workers inside the reservation office and we even told them specifically where the cache was hidden so that they could check in on it from time to time and/or offer assistance to anybody if they are having trouble finding it, although I highly doubt you will have trouble finding this easy one.
From the parking coordinates, follow the path all the way down towards gz, your best approach would be to pass right in front of the sign and continue in front of the main office towards the path that leads you toward the beach area, which is where the cache is hidden. Depending on the time of year, you may have to traverse a 2-3 foot wide stream , however there are lots of big rocks that make crossing this pretty simple.
Lastly, please make sure you replace the cache exactly as you found it so that it remains winter friendly. The cache hide itself is a simple one, all about the journey and the fantastic view from gz...