The Cerberus Fossae are two parallel extensional faults that run almost 1000 kilometres across a young volcanic plain in the Elysium Planitia region. The two trenches run almost exactly parallel to one another and stretch from northwest to southeast. They are extremely steep-sided throughout and in some places cut almost vertically down through the layers of lava. This is an indication that the trenches are still very young, as over time erosion causes rock to break off from steep slopes and edges, so that the gradient of the slopes become increasingly shallow.