** WARNING : THIS AREA INCLUDES UNFENCED CLIFFS OF OVER 200M. PLEASE USE EXTREME CAUTION. NO RESPONSIBILITY IS TAKEN FOR YOUR ACTIONS WHILST IN THIS AREA. **
Blue Mountains National Park is managed by the NSW NPWS. It is open year-round (unless closed due to poor weather or fire danger), with no access fees.
Source - http://www.nationalparks.nsw.gov.au/visit-a-park/parks/blue-mountains-national-park/visitor-info
To reach this Earthcache you will need to walk (or ride your mountain bike) about 5km from the carpark along a well marked fire trail. The final hundred metres from Baltzer Lookout to Hanging Rock is along a well marked walking trail. There is no need to leave the path in order to locate this Earthcache.
Source - https://www.nationalparks.nsw.gov.au/things-to-do/cycling-trails/burramoko-ridge-hanging-rock-cycle-trail
Hanging Rock is an amazing feature of the sandstone cliffs of the Grose River Valley in the Blue Mountains. It is a huge overhanging piece of sandstone, well over 100m high. The block has become detached from the main cliff line. This is one of the most scenic and photographed locations in the Blue Mountains. This location is a drawcard for rock climbers, and also attracts people who’s activities are more on the fringe of adventure sports, slackliners, rope swingers and BASE jumpers.
The oldest rocks in the Blue Mountains comprising the region's basement, are faulted, folded, intruded and lightly metamorphosed rocks formed mainly from marine sediments deposited 470-330 million years ago (m.y.) ago during the Silurian and Devonian periods. Carbonate reefs formed in the shallow seas of that time that have now been transformed into the limestone of the Jenolan Caves and other karst areas within the region. Volcanic rocks, such as the Bindook Porphyry Complex in the southern part of the Blue Mountains National Park, also date from this time (Fergusson, 1980).
Following deformation of the Silurian-Devonian age rocks, shallow marine and terrestrial sediments were laid down during the Late Devonian period. Subsequently, during the Carboniferous, there was a major uplift and a period of erosion before the deposition of the Sydney Basin Sequence.
A movement in the earth meant that the quartzite landscape was flooded by a shallow sea from the east. Streams flowing into this sea carried huge amounts of sediment, which were deposited in horizontal layers. Later, these layers formed rock beds of shales, siltstones and mudstones. In swampy areas around the margins of the sea, piles of dead vegetation were buried under the sediment. They would eventually become seams of coal. All in all, about 500 metres of marine sediments were laid down at this time - between 250 and 280 m.y. ago.
A new phase began with the Triassic Period, 250 m.y. ago. Large rivers began dumping vast quantities of sand on top of the shales, burying them. Throughout this burial process, the weight of the accumulating sediments caused the layers to sink, creating a basin.
Sand collected in the basin, which continued to subside. As the deeper beds were buried, they were forged into hard rock by heat and pressure. Above them, the first layers of sand formed the Narrabeen sandstones (about 200m thick). The sands that followed formed the Hawkesbury sandstones. They were about 300m thick in the central part of the Sydney Basin.
About 170 m.y. ago, the sands stopped being deposited. Forces in the earth started pushing the rock strata upwards. The hard rock layers on the bottom bent and flexed, and the sandstone above them fractured into a series of vertical cracks called joints.
Eventually, the rock layers rose into a broad plateau (and they may still be rising). The plateau was highest on its western margin, reaching elevations of over 1,000m, and sloped down to an abrupt downturn at its eastern edge.
Source - http://www.geomaps.com.au/scripts/bluemountainsoverview.php
To log a find for this Earthcache (optional) take a photo of you &/or your GPS with Hanging Rock in the background, and (mandatory) answer the following questions. (Email answers via my www.geocaching.com profile). Please fulfil all requirements of this cache or your log may be deleted.
- Estimate the width of the gap between the start of Hanging Rock and the cliffline at GZ? Now walk back up and along the cliffline towards Baltzer Lookout. How far do you think it is between this section of cliff and Hanging Rock? Why do you think one is so much different to the other?
- Do you think the small gap at GZ is stable? Why, or why not?
- What natural process do you think caused Hanging Rock to be detached from the main cliffline?