Okay so I am attempting to use the contour tool. I gave it an input raster called "AlmonoNED" and an output called AlmonoElevationContours. I set the output coordinates and extent. However, every time I run the thing it fails saying it is unable to open the mask raster AlmonoStudyArea. This mask raster does not exist nor has it ever existed. More to the point, I do not see anywhere under the environments tab where I can change the mask raster. I have been trying to fix this for over an hour and have made no progress. Any help would be hugely appreciated.