Given the uplift has been going on for about 1.5 to 2 million years, I'd say there has been plenty of time for such. Heck, the Rockies were buried up to their chins in debris and were exhumed over the last ten million years as the region rose about a mile in elevation.
That, if true, would predate the formation of the lakes as a source of water.
Still a great many questions remain. How fast water can erode the stone, how long water has flowed through this particular gorge and a constnat source of water.
I wouldn’t preclude anything just yet.