Now that I am spending more time in Colorado (Carbondale ~6200 feet), I am becoming aware of the challenges of high altitude baking. Before trying an Orange Poppy-Seed Bunt Cake at this elevation, I searched "high altitude baking" on Google and found this useful website. The cake recipe notes adjustments I make when cooking in Carbondale.
In case you cannot download the referenced website at a future date, here is the executive summary:
Some recipes have problems above 3000 feet, others do not. Here are the three major changes to consider:
For each t of baking powder, reduce 1/8 - 1/4 t at 6000 feet and 1/4 t above 7000 ft
For each c of sugar, reduce 0-2 T at 6000 feet and 1-3 T above 7000 ft
For each c of liquid (eggs and butter count as liquid), increase 2-4 T at 6000 feet and 3-4 T above 7000 ft
Increase baking temperature by 25 degrees F.
I also found that using high altitude flour greatly improved my results when making this cake.