No luck, so either it's not a noxious weed or I need more help.
The only thing I found that comes close is halogeton
but that's pretty specific to SE Oregon. But, then again, I found buffalobur
in the backyard, which is also supposed to be specific to the hot and dry part of the state as well.
The strangest thing about it is it seems to start at the little red knot at the middle. This one is about 3 inches across on the widest spot, but I have some that are a foot across. It looks like it just adds length as it gets bigger, so the huge ones have leaves and flowers the same size and such. Here's a closeup
of the tiny little flowers, which are so small I can barely see them. The leaves are around 1/2 in in length, on most of them. They cover the reddish stem the entire length. It grows very close the ground, although the section that gets regular water has some that are growing a little more upright, but still close to the ground. It doesn't like shade much, so I haven't found much of it actually under any plants.
We live in the greater PDX area and recently bought a house with no grass. It has a yard, but no grass. It's coming up in the areas where the weed barrier is either one layer or has a break in it. I suspect this
is a common contaminant in bird feed, as the mourning doves really like to eat it. Heck, the mourning doves could have brought it in from elsewhere even. It spreads through little tiny seeds, about the same size as salt grains, or through runners, in my case, from the side yard clear under the patio (and through the cracks in the patio) to the other side of the yard.
Roundup (glyphosphate) and Quinclorac/Dicamba (Bayer Advanced All in One Lawn Weed Killer) hasn't had quite the effect I'd hoped for. Both are working, but slower than on regular broadleaf weeds.