In March 1901 the Technology Museum, as the Powerhouse Museum was then known, ordered three specimens of the Mountain Ash tree Eucalyptus regnans from a dealer in the Blue Mountains. In 1935 they were transferred to the New South Wales Forestry Department but the Museum kept a section of one of the logs which bore some roughly cut markings on the trunk. These are thought to have been made by Gregory Blaxland, William Wentworth, and Lieutenant Lawson when they crossed the Blue Mountains for the first time.

At some stage the following inscription was painted on the timber sample "Part of the tree marked by Blaxland - Lawson - Wentworth - being the furthest distance recorded in their first attempt to cross the Blue Mountains. A.D. 1813."

The Blue Mountains had formed a seemingly impenetrable barrier to the economic expansion of the colony. Blaxland's discovery of a way over the mountains enabled the settlement to expand the highly profitable sheep industry in the open country on the other side of the range. While there is no record of the group making these particular marks, in Blaxland's journal he refers to the explorers marking their whole route across the mountains "by cutting the bark of trees on two sides."

There is ongoing controversy about the origins of the markings on the 'Explorers Tree' at Katoomba and without concrete evidence arguments may also be mounted about the origins of these markings. It should also be noted that the hard wood of the Mountain Ash would have made it a good choice for making tree markings of the nature described by Blaxland.

References
THE JOURNAL OF GREGORY BLAXLAND, 1813 incorporating... A JOURNAL OF A TOUR OF DISCOVERY ACROSS THE BLUE MOUNTAINS, NEW SOUTH WALES, IN THE YEAR 1813 by Gregory Blaxland, A Project Gutenberg of Australia eBook, eBook No.:0200411. Text first posted June 2002, produced by: Colin Choat. The eBook was checked against a copy of the second edition of that book, which was published in 1870 by Sydney Gibbs, SHALLARD and Co.

Geoff Barker, March, 2007