From the experts:
Aspen is part of two groups of stylish and unique baby names: nature names and place-names. The name of a graceful tree in the poplar family with heart-shaped leaves so delicate they quiver in the gentlest breeze, Aspen is also the name of a trendy Colorado ski resort. Aspen started as a unisex name possibility but now is much more frequently worn by girls.
Aspen entered the popularity list in 1993 and is a good bet to start climbing higher as more and more parents respond to the appealing place and nature image it evokes.