It has various herbal uses but no indication that it produces any adverse skin reactions. Suspect that may have been caused by something else. Purple deadnettle typically is easy to remove. Try and get it before the pinky-lavender flowers go to seed to prevent it spreading everywhere.

Oh my gosh! You got it! Thank you!!! It used to be called baccharis emoryi (here in Zion) , and it got reclassified as baccharis salicina. What threw me off when I looked at your link were the toothed, and wider leaves. But when I typed in baccharis with zion national park, this is what I got! zion/white_wildflowers/baccharis_emoryi_i93.html That's it to a "T"! Tiny flowers with no discernable petals, and elongated, more lanceolate leaves! I can't thank you guys enough! Apparently it's one of the riparian plants here. It must have mistaken my gutter drainage for a wash LOL! Woo hoo!

Ok, think it may be Yellow Sweetclover Suggests removal before seeds are formed so I better get busy!

Eutrochium now. Joe Pye weed. If you could take a picture from further away so we can see the leaf layout we might get the species.