The Peak Range, known locally as ‘The Peaks’, is a chain of prominent and picturesque mountains to the east of Capella which is visible from a considerable distance across the plains of the Central Highlands. It consists of groups of sharp peaks separated by flat plain country similar to the surrounding district. When Ludwig Leichhardt and his party first saw the Peaks in 1845, they were impressed with the ‘noble peaks’ and ‘fine ranges … forming a succession of almost isolated, gigantic, conical and dome topped mountains … spread before our eyes.’ Leichhardt named the individual peaks after members of his party or his sponsors.
The Peaks form a striking backdrop to Capella. They are woven throughout the Peak Downs district’s history - from Leichhardt, who wrote in January 1846: ‘If water were plentiful, the downs of the Peak Range would be inferior to no country in the world’ ; through to the original Peak Downs Station of the 1860s, to the Peak Downs Divisional Board - later the Peak Downs Shire Council, and the Peak Downs state electorate.
The Peak Range district is underlain by an extensive sequence of basalt flows and rhyolite/trachyte intrusive bodies, which were erupted and emplaced between 32 and 29 million years ago (middle of the Tertiary period); probably as this part of the Australian crustal plate drifted northwards across a ‘hot-spot’ deep below in the Earth’s mantle. (Other volcanoes developed later, about 24 to 23 million years ago, as southeast Queensland drifted across the hotspot, to create the Bunya Mountains, the Main Range and the border ranges.) No definite centre of the Peak Range Volcano is evident, so the peaks may represent a line of vents along the crest of the volcano.
Only a thin veneer of basalt (about 30metres thick, with deep soils) now remains on the flat western flanks as far west as Capella and Clermont, but in the range itself remnant hills of basalt flows show that the accumulation was at least in places originally much thicker, of the order of 500 metres.
Three distinct divisions of the range are apparent. The northern and southern parts generally consist of closely spaced pinnacles and domes of resistant rhyolite and trachyte. These were originally plugs that have been intruded towards the end of the volcano and now rise spectacularly from a subdued countryside, eg Wolfang Peak and Mounts Castor and Pollux (the Gemini Twins). Some of the rocks in the peaks have been altered and softened by late hydrothermal fluids, and these parts have weathered more rapidly to give cavernous features such as at Mt Castor and Mt Macarthur.
The origin of some peaks, such as Wolfang Peak is complex, as they possess features of both plugs (steep faces) and of thrust domes (inclined columnar jointing). In general the intrusions of the northern area are composed of rhyolite and pitchstone, while in the southern area trachyte and comendite are more common. Pitchstone is a dark olive-green and splintery volcanic glass that results from rapid cooling of the magma on the side of plugs.
Some of the higher peaks in the southern area, such as Scotts Peak and Mt Roper, are thrust domes resulting from successive intrusions and upheaval of viscous (sticky) lava pushing up the core of each plug.
In the central part of the range, prominent flat-topped mesas and ridges composed of flat-lying lavas rise strikingly above the surrounding open downs country. Lords Table Mountain and the nearby Anvil are capped by a flow of more resistant light-grey trachyandesite or trachyte about 30 metres thick, which overlies about 15 basalt benches. From this it would appear that some quantities of lavas, intermediate in composition between basalt and trachyte, were erupted towards the end of the predominantly basaltic activity.
A good view of Lords Table Mountain and the separated southern extension of Anvil Peak can be had from Huntley Road. A vigorous bushwalk from the road can take you to the saddle between Table Mountain and the Anvil, where the trachyandesite of the cliffs lies on a reddish-brown basalt filled with gas bubbles. The cliffs stop any further ascent for most people. Unusually there is no columnar jointing in the trachyandesite flow; instead there is a myriad of small vertical fractures intersecting horizontal ones along incipient flow banding, resulting in the whole rock mass being shattered into small fragments less than 20cm across. Views from the saddle encompass adjacent ridges where basalt flows can be seen in horizontal layers.
Small undeveloped National Parks cover Mounts Castor and Pollux (Gemini Mountains) and Wolfang Peak (accessible from the Peak Downs Highway); Lords Table Mountain (accessible from the Huntley Road); and the remnant basalt lavas forming non-accessible Eastern Peak further to the south.
Information courtesy of the Geological Society of Australia (Qld Division), GPO Box 1820 Brisbane 4001, from its publication “Rocks and Landscapes of the National Parks of Central Queensland��? by Warwick Willmott, 2006