These are the mountains and pines near Aspen, Colorado.
An interesting thing about hiking in higher elevations (especially if you're used to living in a city that's below sea level) is that you'll feel your aorta pulsating under your bottom left rib. It almost feels like a Keebler Elf is in jail behind your rib and he's punching his way out to make some shortbread cookies.
While a bit unnerving, it's apparently very common and your body eventually begins to acclimate itself to the altitudes after a couple of days. The highest elevation I hiked to at any point was right around 13,100 feet...or 1870 Kareems.