I was going to tell you that it is Daucus carota but now I'm thinking that I shouldn't.

If you still don't have an answer,contact your county's Extension SErvice office as they likely know local weeds better than we do. Salt Lake County Extension Service office ---- http://extension.usu.edu/saltlake/

The little nuts(?) buds(?) are a dark blue green, like broccoli. I haven't found a photo that looks exactly like it yet. I'll go down the hill later and pull a stem and see what I find. Is there any problem with keeping it? I'd think it would help hold the hillside above the bulkhead, like the daylilies do. Or will it invade the rest of my garden if I leave it there?

As far the weed part. It's what I would consider a weedy plant. I grew some in my small garden and I was beginning to spend a lot of time pulling up white snakeroot vollunteers, and I also had the chocolate variation which also spread everywhere like wildfire. This is most common plant in my area, even more numerous than Canada goldenrod, so no need to grow it anyways, not like you never get a look at it. I removed all the plants from that small garden this year, and saved some Ageratinas to be part of a planting at the new, more wooded place because they might hopefully throw the deer off the scent of my other far more special plants. The deer won't go near this plant, they somehow know it's deadly poisonous. I hope they eat those dreadful hostas tho, rootballs and all. Here comes the deadheading lecture I'm sure!