Thanks for your reply. My input data doesn't have a join; it's a point shapefile I created from an excel spreadsheet. The only thing I did to it was reprojected it from GCS to UTM.
I ran the GA layer to Contour. It ran successfully and added a layer to my TOC that appears to have the same range of values as the input GA layer. However, I can't see it! It is not showing up in my map view where expected, under the GA layer, and when I choose "zoom to layer", I end up out in space somewhere. The projection information under the properties appears to be exactly the same between my input data, the contour layer, and the data frame. So the contour layer looks to have data in it, different than the GA Layer to Grid output, but now there is a new issue...or maybe it's related?