Gorge's floor is formed by the uppermost layer of the Bowen Basin, the Moolayember Formation. The impermeability of this layer allows the water generated by Carnarvon Gorge's springs to remain close to, or above, the surface - a significant interplay in terms of the availability of water within the Gorge's ecosystems. Carnarvon Creek, whose flow has only been known to stop twice since records commenced, is an incredibly reliable source of water. In times of drought, it turns the Gorge into an oasis which has supported forms of life long since passed from the semi-arid ecosystems surrounding it. Each of the rock strata exposed in the Gorge erodes and weathers according to its own characteristics, and the variety of soil types and landforms generated goes a long way towards explaining why Carnarvon Gorge supports such a diversity of life. Climate Carnarvon Gorge's climate is considerably different from that experienced in the flatter terrain surrounding it. Average rainfall in the Gorge is higher at 1,000 millimetres per annum and temperatures on the Gorge floor are more moderate. The lowest temperature recorded in the Gorge is -2 °C, whereas temperatures lower than -5 °C are experienced within 5 kilometres of its mouth. Average July temperature range is 6.3 °C – 20.9 °C, and average January temperature range is 20.5 °C – 35.5 °C. Statistically, the wettest month is February and the driest is August. These figures should always be considered in the context of Australia's notoriously unpredictable climate. For example, between October 2007 and February 2008, Carnarvon Gorge received 1,400 millimetres of rainfall; 140% of its annual average. Flora Three broad vegetation types are present in Carnarvon Gorge; eucalypt and angophora dominated woodland to open woodland; mixed eucalypt, acacia, white cypress pine or turpentine woodlands and/or open forests on sandstone slopes, scarps, ridges and residuals; cleared and/or regrowth areas. Four regional ecosystems listed as of concern are easily encountered by visitors to Carnarvon Gorge: Queensland blue gum woodland on alluvial plains; silver-leaved ironbark woodland on alluvial plains; Queensland blue gum, river she-oak fringing woodland on alluvial plains; and tall open forest in sheltered gorges and moist habitats. Two plant species, in particular, are considered Carnarvon Gorge icons; the cycad Macrozamia moorei (no common name) and the Carnarvon fan palm (Livistona nitida). Macrozamia moorei is closely associated with the Tertiary basalt flows of the Buckland Volcanic Province, and is endemic to Central Queensland.