"Forbidden Planet meets Treasure of the Sierra Madre." That was how Steven Spielberg always envisioned the story of The Dig, and Noah Falstein's initial design--which departed in certain aspects from LucasArts' established gameplay style--very much fit that concept. The final game, however, while less innovative in its gameplay, included ideas (both big and small) "borrowed" from many additional sources.
Most of these borrowings emerged in Brian Moriarty's version of the game: his storyline and puzzles included numerous homages to 1950s-60s science fiction B-movies and TV shows, as well as classic SF novels, non-SF literature, and even historically famous works of art. Some of these homages (though by no means all) survived into the final game. Many, though, were deleted when Sean Clark took over the project. Clark massively revised the story and puzzles, in an effort to better fulfill Spielberg's original dictum: create a science-fiction game based primarily on the fusion of two particular film classics.
Forbidden Planet, a milestone of SF cinema from 1956, is a reworking of Shakespeare's The Tempest set centuries in the future, when the United Planets Cruiser C-57D, a sleek naval starship with a complement of around 20, lands on planet Altair IV, investigating the fate of a party of settlers. The crew, led by the heroic Commander John J. Adams (played by a strikingly young Leslie Nielsen), soon discovers the ruins of a long-lost alien civilization, the Krell, which vanished at the height of its glory, leaving behind strange and fantastic machines.
Treasure of the Sierra Madre is another classic (from 1948), but of an entirely different mold. The story concerns three American gold miners in early 20th century Mexico who strike the mother lode on a remote mountain in the Sierra Madre chain. But as none of the miners entirely trusts the other two, tension quickly escalates. One in particular, Fred C. Dobbs (played by Humphrey "Here's looking at you, kid" Bogart), soon becomes deranged and paranoid. Dobbs is convinced that his fellows will kill him for his share of the gold, and, consumed by greed, plans to beat them to the punch. The unbalanced Dobbs assaults one of his companions and tries to escape with all of the gold, but he is captured and killed by bandits; the two survivors, left with nothing but what they had at the start of the film, take their loss in stride.
The debt that The Dig owes to Forbidden Planet is obvious: a spaceship crew from Earth, exploring a remote planet far beyond our solar system, discovers the amazing machinery of a long-vanished alien civilization among the world's desolate ruins. The game's very first version, designed by Noah Falstein, even expanded on the idea by showing several distinct alien cities in various environments. In the Falstein version, which was set centuries in the future, humanity had invented hyperdrive and begun to colonize other planets, but had not yet discovered sentient alien life (much as was the case in Forbidden Planet). The initial plot was that a small starship crew (ultimately reduced to two in the final design document) would land on a promising uncharted planet and explore it, but their ship would be damaged, preventing them from leaving.
Another borrowing from Forbidden Planet can be seen in the background of the alien race. Similarly to the Krell, the aliens of Falstein's game, the Tsevori, had largely annihilated themselves eons before the arrival of humans. In this case, during a devastating war the Tsevori nation of Massic, an authoritarian dictatorship which was losing the fight, released a weaponized plague that killed most of the planet's population. Forewarned about the attack, each nation put its best and brightest individuals into stasis in underground chambers; however, those in stasis could not be automatically revived. The few survivors of the plague were not enough to maintain civilization, and by the time of the humans' arrival had devolved into primitive shaman-led tribes, which had lost all knowledge of the stasis tanks. The primary goal of Falstein's Dig was to waken the Tsevori who had so long ago been put into hibernation. After the humans revived the Tsevori and sabotaged the efforts of the revived Massic leaders to renew the war, they would be rewarded by the other, more friendly Tsevori nations, and would return to Earth bearing a message of peace.
Falstein's concept also incorporated the basic idea, from Treasure of the Sierra Madre, of having tense relations among the starship crew, although the specifics of the character dynamics were different. Originally, Spielberg thought that the astronauts should split into two rival factions, with the drama coming from the conflict between the teams. Due to technical limitations inherent in 1990s SCUMM, the large crew was whittled down to just two main characters, one male and one female, who would have a sometimes friendly, sometimes antagonistic relationship.
The gameplay of Falstein's design for The Dig had several notable features. At the beginning of the game, you would select to play as either Terasov, a male Russian engineer, or Fox, a redheaded female Australian biologist. Which character the player chose would affect how puzzles were solved, giving the game two distinct gameplay paths. After Falstein left The Dig, he would reuse this idea of multiple puzzle strands for the three paths in Indiana Jones and the Fate of Atlantis.
Interestingly, as he himself has noted, Falstein's game also had a few RPG elements, so it was not a pure adventure game. Specifically, it required players to maintain a supply of food and water in their inventory, which would be automatically consumed by the character, in order to stay alive. The two characters would replenish their food supply differently, as Terasov, the engineer, would build mechanical traps to catch animals and filters to purify water, whereas Fox, the biologist, would prefer to live off the land. This mechanic is similar to the gameplay of Sierra's Quest for Glory hybrid adventure/RPG game series, whose first installment came out in 1989, and which required players to maintain food and water in their inventory in a similar manner. The series was critically acclaimed (Quest for Glory I won Computer Gaming World's 1990 Adventure Game of the Year award, beating Lucasfilm Games' Indiana Jones and the Last Crusade) and it's quite possible that Noah Falstein was influenced by it in his Dig gameplay design. (The idea of multiple paths through the game, in which the puzzles varied based on the skill set of the player character selected, likely also came from Quest for Glory. Each game in that series has three distinct gameplay strands; the puzzle solutions depend on whether you play as a warrior, a magic user, or a thief.) However, LucasArts executives were apprehensive about the novel gameplay, and that was a major factor in why Falstein's project was ultimately abandoned.
There was one major literary reference in the Falstein version: the alien planet was nicknamed Ozymandias--like the Percy Shelley poem--because unmanned probes sent back pictures of a broken statue of an alien. This idea was carried over from Spielberg's original "proto-Dig" unfilmed Amazing Stories script, in which a team of far-future archaeologists on a long-deserted planet uncover what is seemingly a statue of an alien--but which is revealed in the final shot to be a statue of Mickey Mouse, as the planet is really Earth and the archaeological site is Disneyland.