The competitors rounded out the action in Herm where Mason cemented his position with a win made even more comfortable when his closest rival went off course near Shell Beach.
In the final general classification, Mason was more than six minutes ahead of Matt Jamieson, who had registered the opening stage victory, with Ben Langlois third.
The leading woman was Jemma Field, after Savannah Goddard was unable to race Herm and Grace Smith picked up an injury earlier in the week.
The field is split into divisions to ensure competition throughout.
Dom Heaume topped Division 2, Simon Touzeau Division 3, Angus Morgan Division 4 and Hannah Pilmanis Division 5.
The 29th All Terrain Challenge is provisionally scheduled for Sunday 20th to Saturday 26th July 2025.