The Moab Grotto is a much younger rock art site than the art work from the Barrier or Fremont cultures.
There are two panels at this site. As you crest the top of the hill you will notice several large rock formations. One will be fenced in to keep cattle out. To find the rock art you must crawl under the rocks and look up and you will see them on the roof of the rocks. I've heard this place referred to as the Cathedral Rock Art Panel.
One of the interesting things about the hike to and around the Grotto site is all of the flint chips laying around. It is ok to look at chips but please don't remove them, let the next explorer have as much fun discovering them as you did.
The Moab Grotto itself is well hidden but not far from the first panel of rock art. To find it from the rocks of the Cathedral walk exactly away from your car to the lowest point water would drain to. Walk uphill here until a small ditch starts to form, get in the ditch and scramble your way up and you will eventually enter a cave which is the grotto. When looking across the landscape you can't see the cave.
This panel is different than most other rock panels in the Arches and Canyonlands area. For starters the artist was not as good as some other petroglyph artist. Second you will notice an image of a horse, this dates this panel to after the time of Christopher Columbus, most other Moab panels are from the Fremont's and is around 900 years old. Barrier Canyon rock art is typically 2000-6000 years old, yes you heard correctly.
Maybe a buffalo or a goat? I personal think that it is a sheep. Wild sheep were once common in the area but mostly died off due to a disease from rancher's domesticated goats.
FYI, the images are easier to see through the screen on your phone than with your naked eye.
Both times I've been here I have seen antelope in the area. They never seem to be too alarmed of my presence but always stay at least 100 yards away.
Inside of the Grotto, its almost a cave and can't been seen from above. In the summer it is cooler than the surround planes. Perhaps this is why the rock art is located here, the area provided natural air conditioning in the desert.
If you are considering a Moab adventure we would recommend checking out the town homes at Moab Adventure Condo. We stayed with them and it was so nice to have room to relax and not be stuck in a cramped hotel room. Since the cost of the rental was split between two families it actually ended up being cheaper than a hotel room and much nicer. Not to mention the pool and hot tub were just sets from our condo.