The great Drought of 1864, 1865 and 1866 scorched up all South Australia north of Mt Remarkable, laid waste the Flinders, and caused damage from which the ranges and the adjoining plains probably have never fully recovered. [Mincham 1983:104]
Goyder’s initial over- assessment of carrying capacity had encouraged graziers to increase their stock numbers and they had overstocked the country.
When the drought struck, settlement had spread beyond the ranges into the saltbush plains. Mines on both sides of the ranges had opened and dray traffic was heavy along the tracks to and from Port Augusta.
The heat was extreme. There were choking dust storms and water sources failed. Hot winds and lack of feed killed off great numbers of stock and native animals.
This affected the Aboriginal people terribly. Their native food sources were dwindling, and they were severely punished if they took sheep for food. They were also pushed away from waterholes, sometimes with vicious violence. Many died of starvation and thirst.
In 1866 a regional Sub-Protector of Aborigines was appointed at Blinman (J. P. Buttfield) to organise relief for Aboriginal people as far as he could.
In the middle of the 1860s drought, Goyder was sent out again to the northern areas. His task was to
lay down as nearly as practicable, the line of demarcation between the portion of the state where rainfall has extended and where the drought prevails. [Mincham 1983:111]
Goyder used the vegetation zones as guides for rainfall zones. Saltbush was the main marker. http://www.history.sa.gov.au/chu/programs/sa_history/sa_dry/map_goyders.htm
After the drought, pastoralists began to run fewer sheep on larger areas of land. Large paddocks were fenced. Shepherds gradually disappeared and boundary riders took their place.