When Garcia is giving the team information about how many kids have died at Jefferson High, she says: "It's like Sunnydale". This is a reference to Buffy the Vampire Slayer. The town in Buffy is called Sunnydale, and the high school is Sunnydale High, built on a hellmouth, which led to a lot of students being killed, hence the reference
Garcia referencing Sunnydale is meta given that series reoccurring actor Nicholas Brendon played Xander Harris on Buffy the Vampire Slayer (1997).