Proclaimed a national monument on 1 March 1950, the Petrified Forest is a collection of fossilized tree trunks. The process of solidification is believed to have initiated around 200,000 years ago with the trunks being washed down a river. The trunks were deposited in rich alluvial sands and isolated from air. This inhibited the decay process and the wood molecules were eventually dissolved by silica molecules, transforming them into stone. This process takes place at a snail’s pace. The largest trunks are measured at approximately 30m, broken up into pieces of up to 2m in length. The sign reads the Afrikaans name "Versteende Woud" on the C39 road north of Twyfelfontein.