Max Tennyson takes his granddaughter Gwen Tennyson to a Plumber's Base underneath Mount Rushmore in certain Ben 10 episodes.
Max Tennyson also takes his grandson Ben Tennyson to the exact same Plumber's Base underneath Mount Rushmore in certain Ben 10 episodes.
Mount Rushmore is where the main Plumber's Base called The Plumber's Bunker is located at.
Cooper and the Tennyson's take on the Negative 10 in the Ben 10 two parter episode Ben 10 vs. the Negative 10 Part 1 and Ben 10 vs. the Negative 10 Part 2.
Mount Rushmore is destroyed so a virtual copy of it created using a hologram device.