Beetle kill Progression

[chris_l]

I made my first trip to Colorado from Michigan in 2016 for archery elk and even though i was unsuccessful I had a blast. Family restraints didn't allow me to go this year but I'm planning to return next year. My question is how rapidly do the beetle killed areas progress and spread. All of the areas we had encounters were relatively close to the areas that died off. Im not sure how often google earth imagery is updated.