The map consists of a large footprint, consistent with the feet of a large theropod.
In the footprint are the remains of a male peasant. He is now a puddle of goo and within the goo is a Stealth Boy.
Behind the scenes
This encounter coincides with the original plot of Fallout, which, according to Timothy Cain during a live conference, involved time traveling and dinosaurs. While these aspects were ultimately scrapped for the new plot that later became the official Fallout game, a dinosaur footprint remained in the final release of the game indirectly in homage to the dinosaurs intended for the game initially in the form of a non-canon random encounter.  It should be noted, however, that while the footprint is in indirect homage, there is currently no substantial evidence linking the two events as the reason for the footprint's ultimate creation and implementation.
- Tycho: "Yeah, I'd stay the hell away from whatever made that. Seriously, I've never seen anything like that. I think our best option is to move on, fast."