Timber was the earliest industry in the Beecroft Cheltenham locality.
Timber was not only needed for the early Colony but was also a product that was included as produce on the convict ships returning, otherwise empty, to England. Timber getting commenced north of the harbour on a large scale, in the Lane Cove Valley in 1802 and the Lane Cove Sawing Establishment at the end of Fiddens Wharf Road, West Killara may have started as early as 1803 and certainly existed by 1807. At its peak 48 convicts worked from that site.
In 1816 the primary government sawing establishment moved to Pennant Hills. This was built at the peak of the hill near the present day water reservoir opposite Mount St Brigid, with subsidiary establishments at Epping (then called Barren Hills which was an apt description following the felling of trees) and Thornleigh. The Epping pit was built in 1819. The Pennant Hills establishment at its peak in 1820 had 100 convicts working from there and 90 at the Epping pit. By 1829 there were only 46 people employee at Pennant Hills and 44 at Epping. Both closed in 1831. Associated with this Establishment was the Government Paddock comprising 40 acres (16 hectares) in what is now Thornleigh. This was used to graze the bullocks used to haul the timber. 1n 1820, 105 bullocks were used at the Establishment.
In addition to the government establishment there were also private operations. Alexander Berry and Edward Wollstonecraft (cousin of Mary Wollstonecraft who was both the author of Frankenstein and the wife of Percy Bysshe Shelley) had a private operation from 1821 to 1828 around Coups Creek which crosses the current day Comenarra Parkway. They had a pit near Hornsby and another near Normanhurst Railway Station. They hauled timber to their private wharf at the end of Blues Point Road, North Sydney.
At the southern end James Devlin, William Kent, Andrew Murray and the trustees for Dr John Savage all used their land grants to commercially fell timber.
Once the trees were cut there were two options for dealing with the tree.
Firstly, they had to haul the log to a saw pit. A pit was dug and the soil mounded to create a working area. The logs were then placed across the pit and sawn into planks or shingles for roofing. One man would stand on top of the log and the second underneath in the pit. In addition to saw pits charcoal was also created by the burning of the less suitable timber.
Secondly, haul the logs either to the Lane Cove River near current day de Burgh’s Bridge and then float them into the city or, from this area to haul them down to the government wharf built at the end of Wharf Road Ermington (or Melrose Park). Again they would then be floated to the city. The government wharf was built in 1817. Some of the sandstone remains of the wharf are still visible. The road was surveyed by James Meehan and built by Major George Druitt in 1820.
A chapel was built at the Pennant Hills Establishment for the Protestant convicts and held about 150 men. It was built in their spare time by their own labour.
In 1819 the amount of work expected of the convicts was increased. While the rations were increased in compensation from 1 pound each of meat and flour per day to a pound and a half the convicts “resisted this augmentation in their labour” and refused to work. This was the first strike in Australian history. The offenders were punished with 100 lashes each.
By the 1860s most of the large timber had been removed. One of the consequences was that the native grasses also disappeared with the consequence that it was less suitable for grazing cattle. The cost of moving timber from the district was, however, still mentioned as a justification for the building of a railway siding in 1888.  There is a photograph of bullocks hauling timber through Pennant Hills as late as 1900.
Saw pits and mills remained scattered through the bush including at the bottom of Malton Road near Argyll place, near Pioneer Track on the Ray property. A saw mill was still operating near the Beecroft railway station as late as 1894. 
 Cumberland Mercury 11 July 1888 p3
 Conversation between R Best and Dr J Hodgson November 2017; Cumberland Argus and Fruitgrowers Advocate, 8 September 1894, 13 October 1894 p 8.