The foothills of mountains that form the northeast boundary of the region, as well as islands in the Kvarner Gulf, are part of the Dinaric Alps, linked to a fold and thrust belt continuously developing from the Late Jurassic to recent times. The thrust belt is a part of the Alpine orogeny and extends southeast from the southern Alps. Geomorphologically the region was formed as the Adriatic Plate is subducted under structural units comprising the Dinaric Alps. The process formed several seismic faults, with most significant among them being the Ilirska Bistrica - Rijeka - Senj fault, which was the source of several significant earthquakes in past centuries. The Dinaric Alps in Croatia encompass the regions of Gorski Kotar and Lika in the immediate hinterland of the Croatian Littoral, as well as considerable parts of Dalmatia. Their northeastern edge runs from Žumberak to the Banovina region, along the Sava River, and their westernmost landforms are the Ćićarija and the Učka mountains in Istria to the west of the Croatian Littoral region.