Described by art dealer Jim Elder as "hugely significant", the watercolour was created by Colonel Light between January and April 1837, around the time he surveyed and laid out the state's capital.

It has spent the past 40 years stored in a camphor wood chest in a garage before being discovered recently by the owner's widow.

Mr Elder said it was nothing less than a miracle that the painting had survived.

"It is a thrilling find," he said. "Its significance is huge."

"This is one of the earliest depictions of Adelaide and thus carries significant weight with historians and art collectors alike."

The work shows a farmhouse with outbuildings and a surrounding settlement of tents and huts with colonists going about their business.

Campfire smoke wafts softly through the gum trees as cattle graze in a nearby clearing.

The Mount Lofty Ranges can be seen in the background beneath billowing white clouds.

Light was a prolific painter and sketcher, often selling his works to support himself, but many of his works were lost forever when a fire destroyed the Land and Survey Office and his adjacent hut in January 1839.

Despite his position as Adelaide's first surveyor-general, he died deeply in debt, having often used his art for income.

He had arrived in the new colony in October 1836 and died just three years later of tuberculosis aged 53.

Most of his known remaining works, including an incomplete self-portrait, are housed in the Art Gallery of South Australia, at the State Library of South Australia and in the Adelaide Town Hall.

This recently discovered painting will be officially unveiled by Adelaide Lord Mayor Sandy Verschoor on Monday.

Australian Associated Press