Gjern Bakker has emerged as an edge in front of a glacier, which has since been cut through the large quantities of melt water during the last ice age. This has resulted in a tunnel valley from Gjern town to Gudenåen.
The hills have previously been covered by forest, although most of it has now disappeared - cut down and used for building houses. Instead, the hills today are covered with a beautiful coat of heather. What remains of the original forest is a bit of oak shrub on the banksides.
In 1893, residents of the area made a suggestion to the Danish Heath Society that Gjern Bakker should be replanted. They believed the area deserved a better fate, due to what they termed an “outstanding natural beauty”. The area has since been planted with spruce and pine.