It's tricky to pinpoint just one "richest" area for dinosaur fossils, as different places are famous for different types of dinosaurs and different periods of history. However, here are some of the most significant fossil-rich regions:

* The Dinosaur National Monument (USA): This site boasts a breathtaking quarry wall showcasing hundreds of dinosaur bones, offering a glimpse into a Late Jurassic ecosystem.

* Badlands National Park (USA): This park is home to numerous fossils from the Late Cretaceous, including Triceratops, Tyrannosaurus Rex, and other iconic dinosaurs.

* Alberta, Canada: This region is known for its wealth of Late Cretaceous fossils, including the famous "Dinosaur Provincial Park," a UNESCO World Heritage Site.

* China: China has become a major player in dinosaur fossil discoveries, particularly in the Liaoning Province, where feathered dinosaurs and other fascinating creatures are found.

* Mongolia: The Gobi Desert is renowned for its incredible dinosaur fossils, including the Oviraptor, Velociraptor, and the massive Saurolophus.

Ultimately, the "richest" area depends on what you're looking for. Each region has unique characteristics and offers a different window into the world of dinosaurs.