For this my guess is Gomphidius glutinosus. It matches the photo and a lot of the text from Mushrooms of Colorado. One difficulty here is that these are young, so no chance to compare to photos of mature specimens.
Looks like a Cort to me, also. Gomphidius glutinosus always has a bright yellow portion of the stipe just below the substrate. check out this photo for a good shot of what I am talking about ... http://www.mykoweb.com/CAF/photos/Gomphidius_oregonensis(mgw-01).jpg