Richard, I apologize for the delay in responding. I tried your suggestions, and here's what happened:
-I think you may be right about overlap in the land disturbance layer. I used the Dissolve tool, and then used the Union of the counties with the dissolved land disturbance shape. That gave me the correct area output for the *total* disturbed land - not the amount of land disturbance per county. I keep playing around with this, because I think you're onto something, but I can't make it work yet.
-Previously, I did use both Intersect and Union. Per your recent directions, I did just of them (Intersect) and got an inflated amount of acres (542,543). I also tried Union and got the higher amount, too. You are correct: with Union, I am just reporting the area of polygons in the land disturbance layer.
-You were right about my projection being wrong. In my haste to follow your prior directions, I had used the wrong (i.e., non-projected) shapefile.
Thank you again for your help. If you have any other advice, I would love to hear it.
Gratefully,
Daniel