The Adelaide Rift Complex (also known as Adelaide Geosyncline) is a major geological province in central South Australia. It stretches from the northernmost parts of the Flinders Ranges, narrowing at the Fleurieu Peninsula and extending into Kangaroo Island, and composes the two major mountain ranges of the State: the Flinders Ranges and the Mount Lofty Ranges. The sediments in the rift complex were deposited between about 870 Ma (the middle Neoproterozoic) to ~500 Ma (the end of the Cambrian).