Complex sentence: These hollows frequently bear traces of processing (seem to be artificially deepened and/or widened); in some cases they resemble footraces, as might be left on a soft surface (hence the name).
Split into simpler sentences: These hollows frequently bear traces of processing (seem to be artificially deepened and/or widened). In some cases these hollows resemble footraces, as might be left on a soft surface (hence the name).