I've never seen a food cache in my 50+ years of beaver trapping.
Get out and trap them little mountain creeks and you'll find them. I've seen plenty of them over in your country, but all I can recall were in ponds in those smaller creeks. I can't recall seeing any over there in the rivers. They often don't use those food caches much if it doesn't freeze up, they prefer fresh veggies, I reckon.