The American South West is a generally more extreme climate.... for both heat and cold.....than the Australian Outback.
Also somewhat drier on average.
The Aussie 'Outback' is really a generic term that encompasses the majority of the Continent, with vast areas of all states and territories except Tasmania, Victoria and the ACT. Aussies consider anywhere west of Woop Woop as being The Outback.
Woop Woop is a fictional place in the same vein as 'Beyond The Black Stump'
The 'Outback' is not just the harsh Central Deserts, can also be the remote and sparsely populated deep tropical North too.
For example, the 'Outback' starts only 10 mins from my suburban Darwin house.
Geographically I would describe all parts of NSW west of the Darling River as 'Outback', all of Queensland west of the Great Dividing Ranges ( in the south east ) and north and west of Rockhampton in Central Queensland. All of South Australia north, east and west of the Clare Valley ( sorta north of Adelaide ). All of the Northern Territory. And all but the settled farmlands of the south west of Western Australia.
So a huge area !
Look up the Northern Flinders Ranges in South Australia. And the Hammersley Ranges in the Western Australian Pilbara.
These regions appear to be similar to the American South west geographically and climatically.
North Flinders Ranges, South Australia
The Hammersley Ranges, Western Australia