FIELD GEOLOGY OF THE SHOALHAVEN DISTRICT (PART 23)

CHAPTER 15: THE CLYDE RIVER VALLEY

Taking its rise at an elevation of 2,500 feet near Sassafras, this small river flow south and descends by way of a great canyon to a level of 200 feet at Yadboro. It does this in less than 20 miles, yet it is a further 40 miles to the sea downstream. This is a peculiar result of the dip of the Shoalhaven group sediments. At one time, these must have extended further south than at present. When the area was uplifted, it was tilted to the north, so that the ancestral Clyde River had to erode its bed against this trend. 

This undoubtedly led to the formation of many waterfalls and the evolution of the canyon upstream from Yadboro. 

The southern edge of the sandstone scarp presents a bold face and is broken into numerous outliers. Some such as The Castle and the Pigeon House are well known to bushwalkers, but there are many others. They all have a similar structure, being capped by cliffs of the Nowra Sandstone or sometimes part of the Berry Formation, with cliffs of lower units below this level. 

The basement rocks are of presumed Ordovician age, flanked on the west by the Devonian group near Currockbilly. There has been some mineralisation and gold has been won from many places near Bateman’s Bay and Nelligen. Some copper and lead prospects have also been recorded. 

This chapter deals mainly with places accessible by road. The numerous bushwalks based on Yadboro have not been treated since they are taken by relatively few tourists. Only the Pigeon House has been included, partly because of its historic and romantic interest, but also because its geology is typical of all the sandstone peaks. 

Excursion 15a 

Yadboro and Pigeon House Mountain (34 miles return) 

Captain Cook sighted Pigeon House Mountain (the Pigeon House or Pigeon Top) on April 21st 1770. At first it was mistaken for a distant island, as only its sandstone cap could be seen. The ‘Endeavour’ was probably off Moruya at the time. Its identity was established the following day and its name given because it resembled the dovecotes familiar to Cook in England.  

Route: Termeil-Boyne Creek-Pigeon House-Yadboro 

Turn right off the Prince’s Highway along Woodburn Road, 4 ½ miles south of Lake Tabourie. 

One mile from the highway, the road crosses a small inlier of slate, which may be examined on the left of the road. For the next mile the road climbs through the lower Conjola Formation and extensive outcrops of siltstone may be seen near the crest of the range. This probably corresponds to the silty member at Point Upright. The highest point in this area, Boyne Trig., is capped by sandstone and this is possibly equivalent to the outcrops at Crampton Island, Bannister Point, and Jervis Bay. 

Turn left on the Brooman road 3.4 miles from the Prince’s Highway and right on the Yadboro forestry road 2.3 miles further on. The base of the Permian is not very noticeable and the road passes over slate country northwards towards the Pigeon House. Stop at Boyne Creek, 4 miles along the Yadboro road. 

Stop 1. Slate is the dominant rock type in the creek gravel, with lesser amounts of quartzite and conglomerate. Boyne Creek possibly carries alluvial gold in small quantities. This creek is the last good place for obtaining drinking water before the ascent of the Pigeon House.  

Continue towards Yadboro. Park on the left where the Pigeon House track leaves on the right, 2.3 miles from Boyne Creek. 

Stop 2. This area was burned out late in 1968 and the road towards Pigeon House became impassable. Before then, it was possible to drive one mile towards the mountain. The vehicular track ends at the bottom of a steep slope, at an elevation of 750 feet. The only rock outcrops at this level are of slate, intersected by quartz veins. 

At the top of the steep slope, the base of the Shoalhaven Group outcrops at 1,200 feet. The Yadboro Conglomerate, full of slate fragments, is the lowest member at this point. Skirt the cliff to the left and climb to the plateau above a few hundred yards further on. By now a fine view of the mountain, a little over a mile ahead, will have opened out. The other prominent sandstone peaks and the Budawang Range have also come into view. 

Outcrops of the Conjola Formation persist towards the base of the mountain until the Wandrawandian Siltstone is reached at a height of 1,700 feet. Fossils occur in this and the lower part of the overlying Nowra Sandstone. Climb up to the base of the sandstone and around the left side to the northern end. The route to the summit (2,361 feet) is clearly marked and involves scrambling up several steep pebbly slopes and scaling a few wooden ladders in the more difficult places. The view is as comprehensive as any in NSW. Perhaps the valley of the Clyde River, immediately to the north commands the greatest attention.  

The entire walk from the road and the return journey takes 4-5 hours. The climb is not difficult except for the final pyramid of sandstone, which would daunt the average hiker. 

NOTE: This is the only place in this work where I think a comment on developments since it was written is essential. In 1971 I led a group of students from Erina High School to this spot. The old route to the summit had been superseded by a set of steel ladders and the track was more clearly marked. This made it possible for many who would have baulked at the old ascent to reach the summit. 

Continue on to Yadboro, where the Clyde River is reached, 6 miles beyond Boyne Creek. 

Stop 3. When subsidence began early in the Permian period (or perhaps the late Carboniferous period), this area was the first to be seriously affected. The earliest sediment to be deposited, the Pigeon House Creek Siltstone, is found only in the neighbourhood of Yadboro, as is the overlying conglomerate. Later on, the whole area west to the Budawang range began to subside and the rest of the marine beds accumulated.  

Yadboro is the centre from which numerous bushwalks radiate. The Clyde River itself may be followed upstream on the eastern side of the bridge. The road across the bridge leads into a network of timber tracks. Yadboro Creek, the western tributary of the Clyde in this area, carries rhyolite and the Devonian rocks derived from the Budawang Range exposures. 

The Clyde River valley from the summit
 of the Pigeon House January 1969 

The Castle from the Yadboro Road 
October 1967

Excursion 15b 

Brooman, Nelligen and the Lower Clyde (51 miles) 

Ordovician basement rocks form the surface over the entire lower Clyde valley. This is an area of extensive gold mineralisation, one where many lonely prospectors hoped to strike it rich but few succeeded. 

Route: Milton-Brooman-Shallow Crossing-Brimberamala-Currowan Creek-Nelligen  

Take the Nelligen road from Milton, as in Excursion 12b. Fine views of the Pigeon House are seen 10 miles south of Milton. Note the contrast with the hills of Devonian rocks in the background. The road from Termeil is passed on the left 13 miles south (see Excursion 14a). Shortly after, the sandstones are left behind and the slate is seen for the first time. Any creeks from here on could yield alluvial gold. 

Brooman, 21 miles from Milton, was the site of a minor gold rush, which led to very little gold being found. The Clyde River presents a very fine appearance alongside the road. Stop at Shallow Crossing, 7 miles from Brooman, where a concrete causeway fords the river. 

Stop 1. Alluvial gold has been dredged from the Clyde in this vicinity, but the amateur prospector cannot hope to find much in a place like this. The gravel in the river includes slate, quartzite, and rhyolite, the latter having come down via Yadboro Creek. 

Turn right along Mare’s Hill fire road, ½ mile south of Shallow Crossing. Take the right branch 4.2 miles further on. Stop at the old mullock heaps by the roadside 0.8 miles north. 

Stop 2. The Brimberamala mines were good small scale producers many years ago. This area is dotted with numerous mine dumps and pitted with shafts. The creek carries alluvial gold, which undoubtedly led to the discovery of quartz reefs on this hill side. Some of the slate shows the interesting effects of extreme folding. 

Either return to the Nelligen road the same way, or turn right from the Brimberamala road and follow the main roads back to the Nelligen road further south (5.6 miles). 

From Currowan Creek, the road passes through pleasant wooded country alongside the Clyde River until the Braidwood road is reached 7 ½ miles further on. 

Stop 3. The slate here is seen to be isoclinally folded and numerous small faults and fold axes can be detected. Quartz veins run through the whole mass. 

At Nelligen the Clyde River is crossed by a fine new bridge replacing the old ferry which formerly operated here. The Prince’s Highway at Bateman’s Bay is 5 

miles further on (see Excursion 13c). 

Pigeon House Mountain from the 
Brooman Road September 1967

Granite-slate contact on the Clyde Mountain 
road September 1967 

Questions 

1. Give an account of the formations met with between Boyne Creek and the summit of the Pigeon House. 

2. Explain the existence of numerous sandstone outliers in the upper Clyde valley. 

3. Suggest reasons why the Clyde River parallels the coast before turning east near Bateman’s Bay. 

4. Granite occurs a few miles west of Nelligen. Relate this fact to the occurrence of gold in this area. Why is gold uncommon in the older rocks north of Brooman? 

The Clyde River ferry at Nelligen October 1963