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otherwise you are going to have to do it via standard clipping, or one of the overlay tools, but you will have to create your boundary shapes to do the subsetting of the larger. As an alternative, you could subdivide your file by querying contours and exporting those. This is essentially changing the contour interval, but given your area, you may want to investigate the difference in the interpolated surfaces to see if it is worthwhile in the first place having a dense contour network. In many situations, reducing the contour interval has less impact on the resultant dem and its terrain derivatives.
