We have Brown Recluse and Hobo spiders in CO which can cause a terrible wound and make you sick for weeks but I have never seen one to my knowledge. I scoop them up and toss them outside alive also.
I have a friend who lost a patch of skin about the size of a hand to a brown recluse bite.
Another friend got bit twice living in a loft apartment at a warehouse.
Found this:
http://www.ext.colostate.edu/pubs/insect/05512.html
Funnel weaver spiders are harmless but are often mistaken for the brown recluse, a potentially poisonous species that does not naturally occur in Colorado. Funnel weaver spiders differ from the brown recluse in that they have a darker brown color with black markings on the abdomen, lack the characteristic “violin” marking on the cephalothorax, have four pairs of eyes instead of three, have striped legs, and are considerably faster.