Hello,

Thank you for reaching out to CSU Extension in Jefferson County. 

From your description and the pictures, I believe your aspen have a canker. Since you described it as "sooty," the aspen may have Sooty Bark Canker. However, other cankers may be the culprit as well, including cytospora. Please review this article about cytospora: Cytospora canker in Aspen – Gilpin County Extension . Here is a description of other common problems found in aspen: aspen.pdf

Do you recall how the tree looked in the spring and summer? This may help identify the problem. Cytospora appears in the spring as an orange spot on the bark. Sooty Bark trees often have leaves that are small and die off quickly.

If you do indeed have Sooty Bark Canker, which from your description, seems to be the case, there are some management techniques.  Managing Sooty Canker | Extension | University of Nevada, Reno

If you have further questions, please contact us.

Thank you,

CMG Shelly