If you mean Acer macrophyllum, no. But it does appear to be a maple/Acer of some kind.

OK, gardengal48, I'm actually up in the PNW, like you, and this hike was in an Oregon forest. I know a lot of forest plants here, but this stuff was just taking over everything.

Maybe an Amur or Tatarian maple?

Still not Acer macrophyllum :-) I am surrounded by scores of big leaf maple seedlings and even whacked-back saplings do not have leaves that look like that. The shape is very different.

I'd guess Acer glabrum, Douglas maple or Rocky Mountain maple.

Thank you. That might fit. Acer glabrum is understood to be a small tree, and I never saw anything really big with these leaves. It also seems to like moist sites, and this was a riparian area. I am just astonished that this stuff seems to be taking over a whole National Forest.

Well, given that Acer glabrum is native to the pacific nothwest, can it really be taking over the forest? Isn't supposed to be there? As in: It is the forest (well, its understory).

There are many natives that are abundant. This one wants to be wholly dominant. Left, right, up, down, everywhere.

Could have been fruiting maples had a mast year and then the big seed-crop had favorable sprouting conditions. A string of good luck for them. False sarsaparilla must've had some good luck in this pic in a nearby forest.