The most dinosaur fossils and the greatest variety of species have been found high in the deserts and badlands of North America, China and Argentina.
Desert environments keep fossils from being covered by plant matter, and without trees and soil, sand and rock are all that stand between an archaeologist and a 100 million year old pile of mineralized dinosaur.
A good dinosaur fossil site requires an area of sedimentary rocks, which are formed from compressed layers of silt and clay laid down over time. According to the "Scientific American book of Dinosaurs" (St. Martin's Press, 2000), dinosaur carcasses may collect where a prehistoric river curved or became shallow, piling bodies in one place and preserving them together.
But not just any desert will do. Local rocks have to be the right age. Dinosaurs lived during the Mesozoic era, from the late Triassic to the early Cretaceous era (from about 220 to about 65 million years ago). To find a particular dinosaur fossil, such as that of a Tyrannosaurus Rex , you'll need rocks about 67-million-years-old in the western United States. Stegosaurus hunters require 150-million-year-old-rocks.
Western North America has been one of the greatest sources of dinosaur fossil finds. Scientists still routinely pull complete skeletons from digs in the Western United States, from Texas to Montana.
A sedimentary rock layer called the Morrison formation is the most productive source of these fossils on the continent, and is where most of the popular dinosaurs, such as stegosaurus and brontosaurus were first found, according to the National Geographic Society.
Dinosaur National Monument on the border of Utah and Colorado marks one piece of the Morrison stone and is a great place to start looking, but other bits of it crop up from the U.S. Southwest all the way up to Canada.
While the United States boasts the greatest number of dinosaur species found, these finds have been spread over much of the country. Canada's Dinosaur Provincial Park in Alberta wins the title of the single site with the greatest variety of species 40 distinct species among over 500 individual specimens have been uncovered there.
A huge volume of fossils has also been unearthed in China, especially in recent decades. According to Paleontologist Phillip Manning's book "Grave Secrets of Dinosaurs" (National Geographic, 2008) a rock formation in the Liaoning province northwest of Beijing is a particularly notable hotspot. The site has hosted 20 million years of early Cretaceous fossils, including amazingly detailed fossils of feathered dinosaurs, like the Sinosauropteryx, that have spurred a scientific re-evaluation of the relationship between dinosaurs and birds .
Got a question? Email it to Life's Little Mysteries and we'll try to answer it. Due to the volume of questions, we unfortunately can't reply individually, but we will publish answers to the most intriguing questions, so check back soon.