The two are super similar, but birch trees tend to grow natively in the Eastern US rather than out west in CO. Also, it's almost too hard to tell from my picture, but the bark was really smooth (not peely) and the leaves were dark green. I'm pretty sure it's an aspen forest, but it's hard to tell sometimes ¯⁠\⁠⁠(⁠ツ⁠)⁠⁠/⁠¯