There are quite a few practical reasons why so many films from the slasher genre's golden era (late '70s, early '80s) are set in the deep woods: the locations are usually just a matter of finding a suitably creepy local park, film permits usually aren't a concern, and lighting & camera setups are often easier to accomplish than they would on interior locations or sets. But for my money, the backwoods make for some of the creepiest environments for survival horror and suspense, ever since the 1971 classic Deliverance had audiences squealing like pigs.
By 1981, Jeff Lieberman had already established himself as a director of unique and entertaining horror films; his bizarre conspiracy thriller Blue Sunshine is a cult classic today, and his gruesome worm-invasion flick Squirm established his skill with queasy horror in a rural setting. Lieberman's horror output thinned out considerably in the years to follow, but he has revisited the genre a couple of times since – most recently the 2004 horror satire Satan's Little Helper. But for my money, Just Before Dawn is the director's best work, and one of the most intense and chilling backwoods slashers ever made.
The story involves a group of twenty-somethings on an RV trip into the mountains to check out a plot of land that one of the group recently inherited. They get the classic slasher-movie warnings to stay away: the local park ranger (George Kennedy), when shown the deed to the land, replies “Those mountains can't read,” and a wild-eyed, drunken hunter (Mike Kellin) seems dead-set on preventing them from venturing up the forest path. Naturally, these warnings are ignored, and the group eventually falls into the sights of a towering, cackling inbred madman and his mountain-dwelling clan. If you haven't seen this one yet, I won't spoil the central plot twist, but there's plenty more surprises to be found, including a shocking change of character that possesses one of the protagonists at the film's climax, and a spooky, well-executed scene involving a lovemaking couple, the killer, and a waterfall.
In addition to some solid performances from Kennedy (whose character dabbles in horticulture and talks lovingly to his plants) and Chris Lemmon (son of Oscar-winner Jack Lemmon), another high point to Just Before Dawn is a chilling score by Brad Fiedel, who would rise to fame as the composer for The Terminator and it's iconic main theme. His central motif here involves a park ranger's rescue whistle, which soars over the treetops accompanied by tense, otherworldly tones, many of which are natural elements electronically manipulated to transform the woodlands into an alien landscape.
Just Before Dawn is available as a decent two-disc DVD set from Shriek Show, which may not be a fully uncut print (though there is a bit more gore than the Paragon VHS release) and shows a lot of of wear and tear, but it's probably the best presentation you're going to see until it makes it to Blu-ray (if ever). It features feature commentary from Lieberman and over an hour of cast & crew interviews, plus photo galleries and more.