I did think of Great Valley Day as a sort of dinosaur Independence Day. It was the day the Flatheads (Apatosaurus) defeated the Two Claws (T-Rexes) and got the Great Valley under Leaf Eater rule.
There is also a Littlefoot Day that commemorates the day that Littlefoot helped bring the Four Kinds Alliance and defeat the Fanged Flatteeth. Litlefoot defeated their leader. The day in question also happened to coincide with Littlefoot’s 25th Star Day/Hatch Day, the day he came of age.
Also, I created an event called the Time of Choosing, which is more or less mating season, where dinosaurs pick mates. The term isn’t brought up until the first part of movie 25, which has the same name as the event, takes place.