I discovered some odd behavior.
Basically I had a "river" mask, which was piped into some displacement. I inserted this
before the erosion shader, as I wanted to see how the river bed eroded with the rest will look. It unfortunately pushed the rivers banks up into peaks in some spots so I decided it would be best to move the displacement below the erosion shader. I cut the shaders, and pasted them (causing TG to automatically snap in the fractal warp shader and terrain shader to snap into the input of the erosion shader automatically), moving them below the erosion shader and than hit "Erode". It sampled, and eroded, but the river erosion remained. Clicking erode again did nothing, it felt there was no change. I had to go into my base displacement PF and change my minimum scale to 0.01 from 0.1 in order for the erosion shader to pickup a change and re-erode, without the river mask involved.
Edit: Additionally, will there be improvements to the river mode? Like a "Alpine River mode" that utilizes Laminar Flows and connects them with river systems in the plains? I've been trying to create alpines like here in Washington State where there are thousands of creeks and streams on our mountains that feed rivers in the valleys, but the river mode seems to favor large intersections for rivers, and don't correspond to erosion that well. See my
post about rivers. I tried using two erosion, and a single with SSS and it looks odd.
For referance, see how the mountains here appear very much like erosion with laminar flows, but the flows all link to rivers in the gullies, which are a bit hard to see due to dense coverage but yeah, you can't walk down that highway without a creek/stream on your left to view every couple minutes. (for some reason it keeps changing the location and is not where I set it, but explore the mountain loop pass there):
https://www.google.com/maps/place/Monte+Cristo+Trail,+Granite+Falls,+WA+98252/@48.0175741,-121.4458161,779m/data=!3m2!1e3!4b1!4m8!1m2!2m1!1sMountain+Loop+Highway+aerial!3m4!1s0x549ac454f42ea135:0x5b9e6c1717613c58!8m2!3d48.0175741!4d-121.4436274