Poison hemlock (Conium maculatum) is a very common plant in North America. In Colorado, it is a List C weed which means it is recommended for control but is not required to be controlled. Due to the increased moisture, populations are higher than normal this year.
If you have it on your property, it is best to control it when it is small. Cutting or removing before it flowers in early summer works well but may need to be repeated. If you are dealing with it once it flowers, you should clip and bag the flowers and dispose of them in the trash. Be sure to wear gloves, long sleeves, and eye protection when handling.