The reason we find so much Amber in Cretaceous rocks is that the Cretaceous period, which lasted from about 145 to 66 million years ago, was a time of great diversity in the plant and animal kingdoms.

A variety of trees, including cypress, maple, pine, poplar, and sequoia, produced copious quantities of resin which over millions of years fossilized into amber.

These resin-producing trees were particularly abundant during this period, and their resins were often buried underground, where they were preserved over time.

In addition, the climate during the Cretaceous period was generally warmer and more humid than it is today, which created ideal conditions for the formation of amber.