Pathfinder Flip-Mat Classics: Falls & Rapids: - Rules of Play says:

Whether your party is at the mercy of deadly rapids or is headed toward a plummet over a crushing waterfall, no Game Master wants to slow the action down by drawing every river bend and jagged rock. Fortunately, you don’t have to! This line of gaming maps provides ready-to-use and captivatingly detailed fantasy set pieces for the busy Game Master. Whether the heroes are in flight or pursuit, this double-sided combat map features rapids, rocky bends, misty falls, and ambush spots aplenty! Don't waste your time sketching when you could be playing. With Pathfinder Flip-Mat: Falls & Rapids, you'll be ready next time your players find themselves up the river without a paddle! A special coating on each Flip-Mat allows you to use wet erase, dry erase, AND permanent markers with ease! Removing permanent ink is easy—simply trace over any permanent mark with a dry erase marker, wait 10 seconds, then wipe off both marks with a dry cloth or paper towel. Each Flip-Mat measures 24" x 30" unfolded, and 8" x 10" folded. On tabletops across the world, the Flip-Mat Revolution is changing the way players run their fantasy roleplaying games! Why take the time to sketch out ugly scenery on a smudgy plastic mat when dynamic encounters and easy cleanup is just a Flip away?