Mustang Grapes are a native wild grape vine that are easily identified by their leaves. The underside is always white.
They are not edible straight off the vine. In fact the acidity could give you burns, which I unfortunately found out first hand.
Once ripened to a dark purple, the grapes can be turned into a fairly good wine or a jelly if you take care to adjust the acidity of the juice. Make sure to wear gloves and old clothing while harvesting. The juice can stain badly and, of course, burn.