If it is a sedge, it reminds me of 3 Way Sedge, Dulichium arundinaceum. It likes wetlands, but really I'm not familiar with all the Poaceae in your area, so it's just a stab in the dark, but it's in your area. I've had it germinate and growing in bog pots, and it hitched a ride in the peat I bought. It should have some wicked rhyzomes if it is Dulichium. I immediately pull them out when first spotted, or else they will completely take over.

When I said your area, I meant somewhere in Oregon, but it could also be hundreds of miles from you. I'm sure you can check into it online. When I look down at 3way sedge the leaves have a mathematical triangle configuration.👀 😵‍💫🤣

It reminds me more of Carex muskingumensis. The leaves seem to be more in a flat plane, than in a triangular arrangement. I don't know if C. m. is native to Oregon, though. I haven't looked it up.

Nice ideas. I did some searching and it looked like a sedge to me too. It is entierly planar, so any sedges with 120° angles between foliage doesnt fit. More later.