The key feature is actually the little slope you can see in profile. That's the flat land above the river being eroded down into the waterway, exposing subsurfa

The key feature is actually the little slope you can see in profile. That's the flat land above the river being eroded down into the waterway, exposing subsurface materials. Some of the rocks had fallen out of that bank and it looked suspiciously anthropogenic. We were already in the area looking along that river because the statistical model of the landscape built up over previous expeditions + other evidence indicated that there should be something to find. There were a number of other sites (e.g. lithic production) found the same way. These rocks in particular were probably to support something like semi-permanent tent poles. As for timing, people had been in the area since the last glacial maximum. I actually have photos of a blade from prior to the LGM in a nearby area, but it has colleagues visible in it. We simply haven't found evidence of people building these kinds of structures much prior to then in that area. I should mention that I'm deliberately underestimating this particular site's age because definitive dating hadn't come back last time I heard and it makes the guessing harder.