The gully to which the city name refers actually exists and is known to be sizable as it provided a gradient negotiable only by bullock wagons travelling through the Mt. Lofty Ranges.
Additionally the gully had permanent freshwater springs which promoted the growth of tea trees in the area – thus the eventual name 'Tea Tree Gully'.

The 350-hectare (860-acre) Anstey Hill Recreation Park is adjacent to the suburbs of Vista and Tea Tree Gully.
The gully to which the city name refers actually exists and is known to be sizable as it provided a gradient negotiable only by bullock wagons travelling through the Mt. Lofty Ranges. Additionally the gully had permanent freshwater springs which promoted the growth of tea trees in the area – thus the eventual name 'Tea Tree Gully'.
The 350-hectare (860-acre) Anstey Hill Recreation Park is adjacent to the suburbs of Vista and Tea Tree Gully.
City of Tea Tree Gully