Ask Mr. Smarty Plants

Colorado State Extension Service has an excellent article, Transplanting trees & shrubs, that recommends transplanting small trees and shrubs in the spring as soon as you can easily dig the soil.  The article also tells you how to go about digging up the tree in preparation for moving it to its new site.  They also have an article, Planting trees & shrubs, that has additional useful information for Colorado residents and a more extensive article, The Science of Planting Trees, that should also be helpful for your project.

It is best to collect Populus tremuloides (quaking aspen) for transplantation before they leaf out. You should realize that aspens growing close together are essentially a clone sharing the same root system so you will have to sever the roots between trees to dig up a single tree.  You should try to get trees from a soil type and elevation that match the site to which you are transplanting them.  Utah State University Extension Service says that success for transplanting aspens is 'fair to good'.

Picea pungens (blue spruce), the State Tree of Colorado, is reportedly relatively easily transplanted.  According to Watson and Sydnor [Watson, Gary W., and T. Davis Sydnor. 1987. The effect of root pruning on the root system of nursery trees. Journal of Arboriculture 13(5):126-130] rooting pruning young blue spruce trees five years before transplanting them essentially doubles the root surface in the root ball so that the trees have a better chance of surviving the transplant.  You probably don't want to wait for 5 years to do your transplanting, but even one year's or a few months' wait after root pruning would increase the root surface by producing new small roots at the cut ends.

For both trees, when transplanting you should consider adding root stimulator.  You can read more advice about tree planting and how to apply root stimulator from Precision Tree Care, Inc.

Your Colorado blue spruces should be fine with all the deer since they are listed in the book, Solving Deer Problems, by H.Peter Loewer, 2002, as being on the 'deer-dislike' list.  However, you might not be so lucky with your aspens since they are in the 'Often Browsed' column in Table 1. Plants and their relative susceptibility to deer browsing in Colorado State University Extension Service's article,"Preventing Deer Damage", by C. E. Swift and M. K. Gross.  There are other suggestions, however, in this article for preventing deer damage.

Picea pungens

Populus tremuloides