Silver Star Mountain consists of late Eocene epoch to Oligocene epoch rock, particularly calc-alkaline volcaniclastic sediment. These rock formations were intruded on the mountain's eastern side by the Silver Star intrusion, a deep stock of granodiorite and quartz diorite that also formed small deposits of copper in the area. Calc-alkaline volcaniclastic sediments, referred to as the Skamania Volcanics, lie nearby and are overlapped by the Troutdale Formation. During the Miocene epoch, these deposits formed hills to the north of the major Columbia River valley, with sufficient height to prevent flooding.