Interesting and good question ~
There is actually no good reason why there should not be whitetails on the Western Slope already, and I would imagine that it is only a matter of time before they will be. I will give it 5 years max.
Their territory typically follows river bottoms and agricultural areas, and as they continue to move into Colorado from the East they have made it all the way up the Arkansas River to Salida with confirmed sightings by the DOW. If they make it over the mountain passes, they will be home free from there...
I would also imagine that we have some coming into the northern part of the State from Wyoming.
Would not be surprised at all if there are a few on the Western Slope already.
Stryker