From a guy who’s analyzed hundreds of miles of stream channels (I’m getting so old), many of them in human-impacted places like this, here goes: The line of rocks is definitely human-placed; and the angular rocks may have some from nearby rock that hasn’t been water-worked. Also in actively-incising/migrating channels in urban areas we see angular bank stuff eroded into streams. The fines/gravel mix is from either a damming episode (either logjam or anthropogenic), or was mixed and placed by a big yellow machine. Probably the cut-off was machine-made, too, and may be related. The historic aerials will tell you an interesting story I’ll bet. And at one/both ends of that dry channel you will find telltale berms/levees built to keep the channel out of it. Hope I get to look at one of these with you some day!
Me, too! I have to say, that’s like the possibility of jamming with Roger Clyne, or writing with C.S. Friedman. I’d go for some of that!
So we’ve an answer from an expert – that’s definitely a human-caused feature. Sweet!
I’m pretty excited by Steve popping by here – I’ve had my eye on one of his stream tables for ages. First thing I’m buying when I finally manage to afford a place with a garage or nice little outbuilding. Can you imagine how much fun it would be to throw neighborhood stream parties? My astronomer neighbor used to have herds of kids over to gaze at the stars through his backyard telescope, and that experience certainly got me enthusiastic about science. A stream table could be just an excellent an introduction. And I have a sneaking suspicion it would captivate a few adults, too. And in an area where stars are all too often blockaded by clouds, but you can see running water almost everywhere you go, it would have the potential to change the way we relate to the rivers around us.
Anyway. That’s one of my dreams. The other is to get out there on the banks with Steve and start speaking River more fluently. Thanks to him, all of us just learned a few more words!