Looking west from Sydney, the Blue Mountains plateau has several prominent lumps, separated by a gorge. No doubt the early settlers examined these with the aid of naval telescopes. Governor Phillip named the northern ones (Mt Tomah, Banks etc) the Carmarthian Hills, and the southern ones (Mt Hay etc) the Lansdowne Hills.
Phillip urgently needed to find farming land. The sandstone country along the coast and to the north proved no good; suitable land was at last discovered between Rose Hill and Prospect Hill. Prospect hill was an important landmark, halfway between Sydney and the Nepean River. Since then, quarrying of the basalt has substantially lowered it.
An expedition up the Hawkesbury to the junction of the Grose revealed much good land, with water access to Sydney providing easy transport for produce. Their immediate problem solved, the mountains offered only curiosity value.
Lieutenant Dawes was curious. He set off from Prospect Hill with the aim of reaching Mt Hay, crossed the Nepean near today's railway bridge, and mounted the ridge. Since he was following a compass course to Mt Hay, and had zero knowledge of the terrain, he was headed roughly northwest. By the time he reached Springwood, he had climbed over several ridges, and negotiated several gorges, in the December heat. Beyond Springwood, it got worse. From Mt Twiss, Dawes obtained a good view of the surrounding terrain. With progress being much slower than expected, and supplies running low, he decided to turn back.
Dawes's report was primarily verbal, and never written down. Still, as he was the first European to venture into and report on the mountains, his journey was of value.
Phillip had what he wanted. Good farming land to support the colony, and an impenetrable barrier to keep the prisoners inside.
Dawes was again in the mountains, this time with Watkin Tench, in 1791. Their objective was to prove that the Nepean and Hawkesbury were the same river, and they climbed to the vantage point of Kurrajong Heights to observe the view.
Next up was Captain William Paterson, a dedicated amateur naturalist, in 1793. His party took canoes up the Grose River, apparently as far as Wentworth Creek. Their interest was botany, and they collected samples of many varieties of wildflowers.
Henry Hacking's route, of 1794, is open to speculation. His descriptions of landforms and vegetation suggest that he reached Kings Tableland. From where he would have had a superb view east; over the lower mountains to Sydney, as well as into the formidable Jamison Valley. They noted the good soil around Springwood, evidence of strong winds, ironstone, and "freestone".