This is definitely Acacia rubida. They were originally planted by me and now are self seeding. They were purchased at Central Tablelands Landcare nursery.
To help with your tree id project, you may like to look at https://www.flickr.com/photos/61627737@N03/albums/72157627244893256/ which shows many of the species on Mt Majura. And see https://majura.org/wp-content/uploads/2011/07/Trees-of-Mt-Majura-2.1.pdf which helps with ids for gum trees.