I used the Define Projection tool to project the Elevation data to NAD 83 CORS96 UTM Zone 10N (all it had before was a GCS in NAD 83) but when I run the slope tool it still comes out all red, except for some some green areas which I believe are lakes. It's the same whether I leave the Z value as 1, 3.048, or 0.3048.
Any suggestions as to what I should try next?