These are flat landforms with alluvial soil that has been created from sediments being deposited over a long period of time by one or more rivers flowing down from highland regions.

As the waterways approach the Barwon River the interconnected streams, as well as lagoons and channels, support extensive flood-dependent woodlands and grasslands".

John Oxley's expedition of 1818 came across the Castlereagh near Coonamble running so high and fast that it was six days until water levels dropped sufficiently to allow the expeditionary party to cross.

[14] Additionally, the catchment area of the upper Castlereagh is criss-crossed with many streams and creeks flowing off the foothills, whose floodwater rushes with high velocity into the main river.

[20] On the upper reaches the most important tributaries, originating in the mountains or slopes, and joining the river before Ulamambri are: Shawn, Gundi, Billy Kings, Baby and Terrawinda Creeks.

Waiting for waters in the Castlereagh near present-day Coonamble to recede, Oxley wrote on 27 July 1818 that "Natives appear to be numerous; their guniahs (or bark-huts) are in every direction, and by their fire-places several muscle-shells of the same kind as those found on the Lachlan and Macquarie Rivers were seen.

"[27] At the time, Oxley's party was camped at the banks of the Castlereagh River, and the spot is today marked with a memorial stone 2 km north of the town.

[28] After finally crossing the river on 3 August and heading easterly towards the Warrumbungle mountains, Oxley wrote the next day: "The natives appear pretty numerous: one was very daring, maintaining his ground at a distance armed with a formidable jagged spear and club, which he kept beating against each other, making the most singular gestures and noises that can be imagined: he followed us upwards of a mile, when he left us, joining several companions to the right of us.

The rich soils along the upper Castlereagh from Mendooran to Coonamble appealed to pastoralists for cattle raising and from the early 1830s Aboriginal people encountered Europeans moving into their country.

Walker lived at Wallerawang, near Lithgow, but held many pastoral licences over vast stations in the Castlereagh River area from Mendooran (where 'Pampoo' was located) to Coonamble.

His response included a single, but telling, comment on the effect of European occupation on Aborigines: "... since stock was first taken out there [i.e. to the Castlereagh] we have abridged all their natural sources of existence.

In his written 1841 response, James Walker also reported that there were usually four or five Aborigines employed on his breeding herd station on the Castlereagh, and that "they milk the cows, bring them home in the evening &c and generally remain on the spot, performing many services which it would be almost impossible now to get white people to do.

[31] James Walker claimed that there were good relations with the Aboriginal people of the Castlereagh River: "... they like uncontrolled liberty and freedom, amongst themselves they appear to have few restraints, they are acute, intelligent and shrewd, and well disposed".

But despite acknowledging that Europeans had "abridged all [Aborigines'] natural sources of existence", Walker expressed the convenient belief that "they appear satisfied to receive our food in exchange for services occasionally rendered us.

More early evidence of the Aborigines mixing and/or working with European shepherds and labourers at the Castlereagh came in 1840 from a ticket-of-leave man named William Jones who was then an umbrella maker in Sussex St, Sydney.

At Gilgandra, an aboriginal woman and her young son were assisted by innkeeper Mrs Hannah Morris to flee their camp at the river bank as the water rose around them.

[25]: 10  At Coonabarabran in 1894 Mary Jane Cain lobbied to have her ownership of her small 400-acre selection, called "Burra Bee Dee", recognised as a place for her people, and others freely moved there.

[41] This route brought his party back to the Castlereagh River at a point south of his first crossing, in an area between the future villages of Armatree and Curban (10 miles apart).

In these early days it was mostly the established pastoralists who had access to land information through their friends and contacts in the highest government levels, and who had sufficient capital to own stock already, or buy more, and who were able to send animals and men up-country with supplies for long periods.

That year, Robert Lowe of Mudgee sent cattle to an area between Gilgandra and Curban on a run he named as "Yalcogrin", also fed by Ulomogo Creek, a tributary of the Castlereagh.

[42] In 1840, convict William Jones gave testimony in court that he had been on the Castlereagh River for eight years and learnt the language of the local people (Wiradjuri); if this was not an exaggeration then he had gone there in 1831 or 1832.

This indicates that at least some of the applicants were already operating in the region: from the area of Mendooran downstream, Richard Rouse applied for "Mundooran", and for Breelong, Thomas Perrie for Eringanerin (later held in 1848 by John Meritt), and James Bennett at "Bearbong" as well as Curban, Robert Lowe already had Yalcogrin, and applied for Carlganda and James Lowe in 1839 for "Warree" further down past Armatree, where Andrew Brown had yet another run "Illamurgalia".

He had with him a small supporting party of men (carrying equipment, measuring with chains, setting up tents, preparing meals) and his teenage son, Henry.

As he proceeded downstream, he noted the pastoral stations he came to, recording first that of Andrew Brown,(Caigan was on the Castlereagh near Binnaway, and Biamble adjacent to it nearer Mendooran) who supplied him with meat for the expedition, and then James Walker's old "Pampoo", followed by "Mrs Hassall's Banduleah" (actually 'Bundalla', on the northern side of the river).

When John Oxley, Surveyor-General of NSW, got to the Castlereagh River, just near Coonamble, with his exploring party on 27 July 1818, it was running a banker on its inside banks.

He wrote: "The river during the night had risen upwards of eight feet; and still continued rising with surprising rapidity, running at the rate of from five to six miles per hour, bringing down with it great quantities of driftwood and other wreck.

[56] At Gilgandra the flood broke the banks in the middle of the night and it was reported that, while it was "hard to tell the immense amount of damage done on the whole river, but what has occurred here is sufficiently disastrous".

The Johnstone family, newly arrived one week, were camped in their tents to take up the 'Castlereagh' run located on flats on the western side of the river immediately to the north of the small village of Gilgandra.

[57] They lost almost all their 800 sheep, most of their cattle and all their belongings, only saving themselves by climbing up a large native apple tree and tying their young children to its branches with ropes so they wouldn't fall in.

Thirty years later Mrs Johnstone recalled the dreadful din of the water and the huge number of dead animals, parts of buildings, and fencing being carried downstream on the swirling floodwaters.