Here you go:
Not specifically for Gruber other than it is located in Braggs, OK. When I said Chandler I meant Clayton, my apologies. I edited my post above. Chandler is a small local place near Tulsa. I don't recommend you make the drive.
Green Acres ORV Park in Calyton, OK is cool too. Typing the names of these places into you tube will bring up videos of people wheeling there. Dont be discouraged when some of the videso are crazy. There are typically plenty of trails that are "relatively easy" at any of these parks.