In October 1877, with a companion, Sam Croker, Buchanan began to investigate the country from the known regions round the Rankine to the overland telegraph line, around away. They discovered much good new land, part of the Barkly Tableland, and has since carried some of the largest herds in Australia. Throughout the 1870s and 1880s Buchanan did a large amount of pioneering, working principally in northern Queensland and the Northern Territory. Buchanan was also noted for his overlanding feats including droving 20,000 head of cattle from Queensland to Glencoe Station. He had another property, Wave Hill, for a period, but he lost this in 1894 on account of a great fall in cattle prices and the difficulty in getting markets. His son, Gordon Buchanan, had taken up land at Flora valley in 1887 and Buchanan now established this as his headquarters. About two years later, with another man and an aboriginal boy, he started with camels and equipment provided by the South Australian government to find a stock route from northern Queensland. He went from Oodnadatta up the line to Tennant Creek, and then westward to Sturt's Creek. About from Hooker's Creek he sighted the hills now named Buchanan Hills, and next day came to a branch of Hooker's Creek. Then he went to Hale's Creek and the Sturt, and then to Flora valley. Attempts were made to find a practicable stock route to the west with no success. Returning to Flora Creek he prepared a report for the South Australian government which added much to the knowledge of the country, though Buchanan had failed in his main object. In 1899 Buchanan, now 73 years of age, bought a farm on Dungowan Creek, from Tamworth and he died there in 1901 still working. Nat was buried in the general cemetery at Walcha, New South Wales. He married in 1863 Catherine Gordon who survived him, along with a son.