To insert, or to, more appropriately, THRUST the fist, shaped like a rock (boulder) into a sexual area of the human body. Once fully inside, the hand is to mimmick the movement of a large boulder and/or that of a crumbling rock, creating a sensation of both pleasure, and pain for the receiver. It is said that geologists (those who study rocks) can supply the best Boulder Colorado, as they can reenact the boulder with the greatest skill out there. Commonly practiced in the town of Boulder, Colorado, this trend is being spread throughout the world, known for its creativity and distinctive pleasure.
R: Hey maxdog, what did yu do to ashleymae last night?
S: Yo dude, he heela Boulder Coloradoed that shit! Beat that pussy up!