Mark Trail was an American newspaper strip, one of a number that were reprinted in British comics in the 1950s. Although enjoyable, the reprints never seemed to quite work -- pasted up they looked like a normal British comics page (which had a rather regimented look at that time) but the pacing of a daily strip was slightly off, something you adjust to if you're reading a reprint that admits to its newspaper origins; I've been reading the latest volumes of James Bond reprints from Titan over the past few evenings and haven't noticed a problem.
Mark Trail appeared featured in three adventures published in Knockout in 1951, the opening storyline seeming to concentrate on Andy rather than Trail's job as a forest patrolman. This doggy theme was continued with the second story, 'Billy's Dog Wagger'...
... although the third storyline was concerned with grizzly bears rather than grizzly children. The character in the original storylines wasn't a forest patrolman, per se, but a photographer and writer (for Woods and Wildlife magazine) who has to deliver a dog (Andy) to 'Doc' Davis and his daughter, Cherry, who live at a wildlife sanctuary called the Lost Forest.
The Mark Trail strip was syndicated by the New York Post and was created by Ed Dodd, first appearing in April 1946 and initially appearing in 45 newspapers. According to Dodd's entry on Wikipedia, the strip was scripted by Dodd and drawn by Tom Hill, enjoying its greatest success in the 1960s when it was syndicated to around 500 newspapers. This brief description is expanded upon by Steve Gurr (in the New Georgia Encyclopedia), which reveals that "Dodd's syndication success created the need for assistants. He hired Jack Davis (who later became famous for his Mad magazine art), Tom Hill, Rhett Carmichael, and Jack Elrod. Dodd turned chiefly to writing the narratives while his assistants did the artwork." Elsewhere (here, in fact, at a gallery exhibition of Mark Trail artwork), we learn that "Tom Hill joined Dodd on the Mark Trail adventure strip in 1948 as an illustrator. In 1950 Jack Elrod joined the team."
It would be interesting to know if anyone recognises the period from which the above strips date (1946-51... that much I can guess myself!) and whether these are indeed drawn by Ed Dodd or by one or other of his assistants.