Bricks, Masonry, Asphalt and Concrete - river rock

What is the easist way to remove river rock from a driveway.There is concrete underneith the rock

When you say river rock, what exactly do you mean? Is it that pea gravel/epoxy overlay material (some call it chattahoochee stone) or is it like flagstone mortared to the concrete? How thick a layer is it?

its the pea gravel with the epoxy overlay.Is less than a half inch thick

You could rent a walk-behind scarifier from a rental yard. It has little teeth that chip away the top layer. It's like what they use to grind asphalt off a road surface before they resurface, only on a smaller scale. The trouble is that it will likely chip off the top layer of concrete as well if you're not careful. Another downside is that it will not take every little bit off unless you DO get into the concrete surface.
Another option is a scraper on a long handle. You may be able to wedge it between the epoxy rock and the concrete and chip it off in sheets. Really, there's no good way to get it all off.
To get the last remnants of epoxy off the driveway after scraping or chipping, you'll have to use a chemical epoxy stripper. However, since the biggest use for epoxy rock is to cover bad concrete, my guess is that the concrete under it is in bad shape to begin with. You would probably be better off just tearing the whole thing out and replacing it. I personally think that epoxy rock is about the worst thing one can cover concrete with. I've never once seen a job that lasted more than a few years.