Colin and Hassan followed her to a six-foot-tall obelisk—a kind of miniature Washington Monument—before which la’ a plethora of not-new pink silk roses.
John Green -- An Abundance of Katherines
a stone pillar having a rectangular cross section tapering towards a pyramidal top
More rarely, obelisk references a character used in printing to indicate a cross reference or footnote. The character looks a little like a dagger or cross. (See Wikipedia - Obelisk (typography) for pictures.)