Here's a good demo. In NY we used 6" or 8" rubber worms for this and routinely dragged out 5 lb. bass. Frankly I'm not sure what would be best in CO, but I'd go with 6" or so. The guy in this video uses a 12" worm which is HUGE.
Here's a few pix of what I have on hand:
Note that you need 3 things for this rig: the cone shaped weight, the hook and the worm. The hook in this pic is a little small for this rig (all I had at the moment), but you get the picture. We always used straight shanked hooks, not the off-set ones that the guy in the video used. But they are probably just as good.
Here's what it looks like with the hook in, but not on a line, obv.
To keep it "weedless" you push the tip of the hook through the body of the worm until it just barely comes through. That way it won't snag on weeds.
To work these jigs, we would cast the rig out and let it sink to the bottom. Then we would reel in a few feet and stop, giggle the worm a time or two, then reel in a few feet, giggle a time or two, over and over again. Best bass set-up I ever used. Good luck!