The Euganei Hills are of volcanic origin; the first eructions of basaltic magma occurred during the Eocene period, when the area was submerged under the sea. Later, in the Oligocene period, eructions of more viscous rhyolites, trachytes, and latites created the typical volcanic cones.
The area still maintains geothermal activity (hot springs, hot mud) in the spas areas of Abano Terme and Montegrotto Terme.
The Colli Euganei remained a small archipelago until the general rising that generated the entire Pianura padana during the Quaternary period.
The area is now a protected regional park. Near the Hills are the towns of Este and Monselice.