The mystery of the Land of the Lost deepens in "Downstream," as Rick Marshall leads his children on a rafting expedition downstream to see if they can find a way out of the land.
Along the way the episode sets up a number of mysteries about its setting. First is Jefferson Davis Collie, a Civil War artilleryman. Second is the cave where he lives and excavates jewels that store and direct large amounts of energy, enough that Rick speculates that they may be the power source for the time portal that brought theme there. Third, the show establishes that the land is finite and self-contained; heading downstream ultimately just leads back to the same point. Lastly, this is the first episode to mention Pylons.
As episodes go, this one was lackluster and not particularly exciting. But it does reveal just how intricate a world David Gerrold had created as a setting for the show. It's no surprise that 40 years after the show aired, my daughter right now is creating her own pretend Land of the Lost.