Augustus C. Gregory, a surveyor, was the most distinguished of three exploring brothers. His explorations included expeditions in Western Australia (where he discovered and named Lake Moore), Queensland, and Northern Territory (where he discovered and named Sturt's Creek, which he traced for 300 miles).

In March, 1858, he led an expedition to search for Leichhardt's party, which had disappeared without trace in 1848. The party set out from Euroomba Station on the Dawson Ranges. After travelling for four weeks he found the letter "L" cut into a tree, and thus encouraged, he followed the Barcoo River to its junction with the Thomson River, and then proceeded along Cooper's and Strzelecki Creeks as far as Lake Blanche. He arrived in Adelaide in July, 1858, without having found the missing expedition.

The information recorded byA C Gregory on this journey was, however, of great value, and had the effect of reviving South Australia's interest in the country north of Lake Torrens.

His journal was published in 1884, covering his journeys and those of his brother, Francis Thomas Gregory (1821-1888).