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Dipper, Mabel, Soos and Stan were in an abandoned mine, looking for Waddles who was snatched by a pteradactyl. They followed a trail left by the pig's unfinished sweater, right into the crevasse, which was underneath an equally abandoned chapel, where they were joined by Old Man McGucket. The five soon found out that it wasn't just another abandoned mineshaft, for it had geysers and prehistoric flora and fauna. Soos had gotten too close to an ancient flower and had his sense of smell affected by its acid spray.
Dipper was leading the way, with a lantern in his hand. The ambient light shone on a large wad of amber encasing a Tyrannasaurus Rex. The frightening sight caused everyone to scream. After they regained their composure, they explored more of the caverns, where they noticed more amber wads and the dinosaurs in them. The five all gasped in amazement.
"They're trapped inside the tree sap!" said Dipper as they walked past all the accidental exhibits. "That's how they survived for 65 million years!" He then stopped by a pile of sap with an empty cavity, shaped like a pteradactyl. "Whoa." He shone his lantern on a melting part of the sap. "The summer heat must be melting them loose!"
Dipper then walked on to where he noticed something out of the ordinary, even for such an environment. There was a small sap pile. Inside was what looked like some kind of saber-toothed squirrel, as well as an acorn. It appeared to be running towards the nut, when both were trapped by the amber. Dipper stretched out his lantern to get a better view. He rubbed his chin with his free hand, wondering how it got into this predicament.
"Holy moley! Forget the cornicorn," Stan said as he stopped by a triceratops. "This is the attraction of a lifetime! I could bring people down here and turn this into some sort of theme park!" He could picture it in his mind. "Jurassic... Sap Hole!"
Soos then noticed a velociraptor, which had one of its digits on a claw sticking out of the amber. The finger was wiggling, and it wouldn't be long before the entire claw would be free. "Uh, dudes..." he pointed to it as Dipper came over.
"Maybe... we should keep moving." He motioned for the others to walk.
Credits to markmak of DeviantArt for creating such a wonderful crossover fanart.