The Jura Mountains were formed during the Miocene epoch, specifically between 23 million and 5.3 million years ago. This period of mountain building is known as the Alpine orogeny.

Here's a breakdown:

* Alpine orogeny: This was a period of intense geological activity that resulted in the formation of the Alps, Pyrenees, Carpathians, and the Jura Mountains, among others.

* Miocene epoch: This epoch was characterized by significant tectonic plate movement, leading to the collision of the African and Eurasian plates. The pressure from this collision caused the Earth's crust to buckle and fold, ultimately forming the Jura Mountains.

It's important to note that the Jura Mountains are a relatively young mountain range compared to older mountain ranges like the Himalayas or the Appalachian Mountains. They are still being sculpted by erosion and weathering, which continues to shape their landscape.