|Image from Southwest Colorado Wildflowers.|
Westcliffe botanist Christine MacLeod explains all here.
"During the drier years, seeds from many of our high prairie plants, including purple mustard, chose to remain dormant in the soil, contributing to a rich seed bank for years to come. Seeds can stay in dormancy for many years until the conditions are optimal for sprouting. And that is just what they all have done these past few weeks."
It's another invasive Asian species.