Who knew a weed could prompt such a vigorous conversation!?!?
It got uppity over the weekend (e.g. it grew taller than me), so I reached out in a fit of rage and pulled it!
It came out surprisingly easily. Its root ball was only about 12" in diameter, and not very deep at all. It probably grew as tall as it did because of the drip watering. I saw a few of these around the neighborhood, on the sides of the street, etc, and they were only 1-2' tall.
I got it before it flowered, so I don't think I'll have a mass recurrence next year. And if I do have a few solitaries, I'll know what they are avoid tending them so carefully.

Sunset 23/USDA 11a, Elev. 783', Frost free since 8,000 BC. Plagued by squirrels, gophers, and peafowl, but coming to terms with it!