Took more pics - and pulled it out!! :) I don't think it's either of the above, because the leaves alternate along the stalk instead of a group at the base... The root was weird, too, almost like a sideways carrot or something...
That Looks Just like...
Mountain Orach(Atriplex hortensis).
It Grows 4'-6' Tall.
Heavy Seeder and as the Season progresses
the Plant will turn the Most Beautiful Fuchsia-Magenta Color.
I have Several Plants of it Growing here now.
It's Totally Green for about 2-3 months,
And then begins a Slow Process of the late color change.
Here in Oregon it happens in late Aug/Early Sept because of our Cooler Summer Climate.
I'm not so sure it's the Mountain Spinach, either!! The leaves were thinner, very green except for bright red tips, the Atriplex Hortensis had those beautiful purple leaves...didn't find any pics of those going to seed - wow, wonder what I had there (I'm thinking of getting some seeds off the one I threw away, just in case!!)