18.75x23.75" onionskin sheet has original pen and ink watercolor art depicting concept design for Marx playset that eventually became the "Prehistoric Mountain" playset #3414. c. early 1970s. Design features dual volcano mountaintops (one active, one inactive w/hidden entrance), underground water caverns and an "Albino" Triceratops figure. The final design of the playset that came to be "Prehistoric Mountain" differs somewhat as the volcanoes were eliminated in favor of a regular mountain design. Sheet has been rolled and shows lt. handling wear. Exc. Nicely detailed art. Unique.