If you have a DEM, you can create the contours using Spatial Analyst tools. You just have to make the vertical interval small enough that they show up. If the depression is small, a large vertical interval might miss a depression unless the depression happens to be at an elevation that is right on the contour interval.
The contours are lines. I suppose if you convert the layer of lines to polygons, probably only those polylines that close will be converted to polygons. You can then visually see the depressions as polygons. I assume their area would be small and you could search for the polygon with the smallest area. Hill/mountain tops will also have small polygons.
