Within the park the Plenty River is the dividing line between two distinct geological types, the western side is basalt and the eastern side is sedimentary rock. This provides Plenty Gorge Park with a wonderful diversity of vegetation communities and habitats, and it is recognised as being one of Greater Melbourne's most important refuges for both threatened and regionally significant species.
Plenty Gorge Park has become an oasis for many native fauna species. Kangaroos, echidnas, and a variety of skinks and snakes are frequently seen in the park. Many frog species frequent the low lying areas of the park including the endangered Growling Grass Frog. At night, possums, bats and owls are a common sight. The lakes and wetlands provide habitat for a number of different bird species. Wood ducks, grebes, swans, Black Fronted Plovers and even Japanese Snipe can be sighted from time to time. Perhaps one of the most spectacular species to be seen soaring over the park are the huge Wedge-tailed Eagles.