Not sure what it is, but I don't think it's a maple at all, nor an elder - some of the leaves are bipinnate (the basal leaflets themselved pinnate: see lower right leaf in 2nd pic), which maples and elders aren't.

Last pic, yes, a species of Ribes.

Resin

It's not Boxelder, Acer negundo

Yes, its possible that it is a box elder. They seem to volunteer quite readily. But I'm not good at id'ing pics. Sometimes boxelder has leaves that appear bipinnate because of they are highly lobed, possibly from the vigorous growth this speciman has put on.

If you collected the seed, then its probably native to where you acquired it.

May well be the maple you wanted.

Rocky Mountain Maple

Some young plants deviate a little bit.

Mdvaden, I did collect seeds up in a nearby canyon, and I left them in small pots outside for the winter to stratify. And this was the only pot (out of five or so) that actually developed a seedling. But I'm wondering if a seed from a Box Elder tree in the neighborhood perhaps made its way into my pot and it that's what sprouted instead of my collected seeds.

I did see a photo online tonight showing an Acer glabrum with some pinnate leaves. Here's an example from bioed.org:
{{gwi:406535}}

Don't know if mine is similar enough to that photo. Any further thoughts?

The acer glabrum pic may appear to have pinnate leaves, but its just deeply lobed leaves which gives the illusion of pinnate. The same thing pineresin saw with the possible box elder you have.

trust me, after cutting down over 20 large boxelders in my yard, and still dealing with seedlings and resprouts, the top pics are definately NOT box elders. The strange leaf shape may be a random mutation in the seedlng's dna. Or, If box elders were growing in the area of the rocky mountain maples from which seed was collected, there could have been some cross-pollination, resulting n your seedling. Our box elders used to cross pollinate with a red maple tree, creating red box elders and other oddities that were even weedier than the box elders alone.

I agree with bdude4, that does not look like the dreaded Acer negundo. I have more than a dozen in my yard & I know what they look like, from seedling to overgrown monster.

The tall seedling is boxelder, Acer negundo. It has a transcontinental range and is different looking in the west than the east. For example, in the east is is largeley a 3-leaflet leaf and in the west 5 leaflets. Note the opposite leaf arrangement. The other is a Ribes. Note the opposite leaf arrangement and the venation pattern -- very unmaple.
Yes, a deeply lobed leaf becomes a compound leaf in Acer -- very common in Acer glabrum.

So, I'm not getting a strong sense of confidence here about what it is! Some say it's a box elder and some say no. Hmmmm.... If it weren't a box elder, what else could it be?

I'm leaning towards thinking it's a box elder. It has a similar leaflet pattern to a younger seedling I was growing (from a volunteer plucked out of my flowerbed) for a while that someone else here identified as a box elder -- Acer negundo. Here's the younger one that I threw away last month:

{{gwi:382882}}

It's not exactly the same as the bigger one (the small one had three leaflets and purplish stems), but I think the leaf pattern is similar enough that these may be the same species.

And the fact that the big one grew six feet in one season is making me think it must be some aggressive junk tree, too!

Still, there is some doubt here. So if anyone knows whether the big one might be a better tree than Acer negundo, speak up and save its life before it gets the dreaded shovel-o'-death!

Sorry if I added to the confusion. I had no idea that boxelder in the West had different leaves. The thing in the last photo looks suspiciously boxelderish. I say haul out the shovel!

In my earlier post I meant to say Ribes has an alternate leafing pattern, not opposite.