Land of the Lost - 1x04 Downstream

Attempting to escape the Land via the river, the Marshalls reach a vast cavern in which lives an elderly Confederate soldier.
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The Marshalls build a raft and head downstream in search of civilization, with the hope of finding a way back to Earth. The raft comes to a waterfall where they are forced to quickly leap into a cave.

Inside they meet a crazed man who identifies himself as Jefferson Davis Collie III (Walker Edmiston), a Confederate artilleryman. Collie forces them to mine the glowing minerals of his cavern to earn a meal. Rick hypothesizes that the lode may be a radioactive power source which causes the opening of time portals.

Collie explains the peculiar properties of the minerals (such as that a red and a green crystal together make a bright light, and an added yellow crystal creates a blinding but short-lived light) and tells of his experience shooting and eating three Sleestak. He explains that the river travels underground, but refuses to tell the Marshalls if and where the river comes up again, explaining that he is starved for company and wants them to stay.

Three Sleestak appear with crossbows, but Collie scares them off with rounds from his cannon, "Sarah." Out of water, Collie heads to refill, and the Marshalls sneak after him. The four are ambushed by Sleestak, and Rick puts a red, green, and yellow crystal together, creating a blinding flash that dazes the monsters. The light quickly dies, however. Will grabs a blue crystal and a green crystal, which together make a bomb which explodes around the Sleestak.

The Marshalls and Collie escape into the river, and head downstream. Eventually they find themselves in a swamp, and recognizing the Pylon, realize the river runs in a circle and has led back to their own part of the jungle. Rick supposes the jungle is impossible to leave without a time portal, calling it a "closed universe." Collie, frightened by the dinosaurs, decides to return to his cave.

http://en.wikipedia.org/wiki/Downstream_(Land_of_the_Lost)