"soft or marshy place," 1530s, of unknown origin. Also as a verb, "to become soaked; to soak" (mid-15c.), perhaps related to soak (v.) or from or related to similar words in Scandinavian.
Examples from the Web for sog
Las' summeh's sun neveh fazed it 'cept to sog it down all the mo' solid.Connie Morgan in Alaska|James B. Hendryx