The Collaborative International Dictionary of English v.0.48:

Trek \Trek\, v. i. [imp. & p. p. Trekked; p. pr. & vb. n.
   Trekking.] [Written also treck.] [D. trekken. See
   Track, n.] [South Africa]
   1. To draw or haul a load, as oxen.
      [Webster 1913 Suppl.]

   2. To travel, esp. by ox wagon; to go from place to place; to
      migrate. [Chiefly South Africa]

            One of the motives which induced the Boers of 1836
            to trek out of the Colony.            --James Bryce.
      [Webster 1913 Suppl.]