Question
I am wanting to plant a tree, preferably a flowering tree, in a field as a type of memorial to my 8 year old nephew that was lost to us this summer due to a hit and run accident.  I will not be able to get the tree water regularly and it is in an area that is fairly secluded.  We live in zone 5 in Colorado and a drought resistant tree would be good since summers and winters are questionable when it comes to rainfall and moisture.  Any help would be appreciated!!

Answer
According to the Colorado trees.org Callery Flowering Pear
might fit what you want.

http://www.coloradotrees.org/treeomonth/2003/march_03.htm

I would suggest you contact the Colorado State Forest Service and ask one of their Foresters to help. They can give local tree information and may even be able to visit the site and advise you on the best tree.
Their web link to the contact page is:

http://csfs.colostate.edu/localforester.htm