I don't know of any evergreens that grow crazy fast in Colorado. However, some grow faster than others. You might take a look at the link I've provided from CSU for information on the growth rates of various evergreens.

If you're looking for a temporary screen with fast growth, you might consider a large, tall shrub. You'll find information about shrubs in CSU Fact Sheet 7.229 - Xeriscaping: Trees and Shrubs at http://www.ext.colostate.edu/pubs/garden/07229.html.

Here is a link that might be useful: CSU Fact Sheet 7.403 - Evergreen trees

The crazy fast growing tree can be deciduous, does not have to be evergreen. Excited to see ideas from this brilliant forum :)

The only tree we've planted that seems to grow fast here is crabapple. We planted a 6' tree when we moved in 4 years ago and it's probably twice that now. Definitely have that perenial "1st year they sleep, 2nd year they creep and 3rd year they leap" thing going on in CO!

Fast growing usually equals weak wooded. Is it your plan to take down the fast tree once the spruce reaches some size?
How close to the spruce's planting area will the fast tree go?
What's the site like, as in what exposure, slope, amount of sun and soil? Any chance of a pic?

Barb

I'd be tempted to go with the spruce and work on amending the soil and keeping it watered for maximum growth. They can grow pretty fast, once the roots are established. I have one hitting 15 inches a year in both height and diameter.

If you have the water and want to plant a weed, try a cottonless-cottonwood. If you keep the soil wet, that thing will do 5 feet a year.

If you're looking for a crazy-fast deciduous tree, you could also plant a honeylocust.

Don't know how large you want it, but we're growing a Seven Sons for beauty but it happens to be extremely fast growing too.