hoping to identify stinging plant
You may address this nasty plant as Canada Thistle. It is a thug.
CSU Master Gardener Boulder County has a fact sheet on the Canada Thistle. I am an apprentice and this is my 2nd time on the desk so I beg your forbearance as I am unsure if, the link below will access the fact sheet.
Ask an Expert is available to you at any time. If, you have further questions in addition to the identification of the plant please contact us again. I hope this helps.
Add my curse too!
It definitely looks like a type of thistle. Often thistles have bright pink flower heads.
With the picture, its hard to see but I think I can see a small yellow flower head, if so
it could also be a type of Sowthistle. The stem would also contain a milky juice.
Thistles are considered a noxious weed in colorado.
Watch it mature to see what color the flower head is.
Thanks for the quick replies. I'll post another picture when it blooms. Actually, I should have include something for scale -- I think it's small compared to Canada thistle (this is "adult size"). The leaves don't quite look like sow thistle pictures on the internet, but there's a lot of variation.
A more mature picture would be very helpful in determining the type. The flower color is important.
Found it: desert tragia, or branched noseburn! What a name. Apparently some varieties sting more than others. https://www.backyardnature.net/n/h/noseburn.htm