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I did a search for spiders in Colorado and came across this:
Dysdera crocata (Wood Louse Hunter)
This hairless spider is perhaps best marked by its large fangs which it uses to feed on pillbugs (roly-polies) and other hard-bodied prey. When full grown they are about .5 inch in length. Dysdera have a generally creamy gray body with distinctly reddish legs and cephalothorax. They live in a silk retreat and hunt at night. Their bite can be painful but they are not aggressive. Their venom is not known to cause medical problems.
The photo is not very large, but the spider looks similar to yours.