The Westmoreland Conglomerate is the oldest formation of the Middle Proterozoic Tawallah Group, the basal group of the McArthur Basin sequence. It unconformably overlies Early Proterozoic granite, acid volcanics and metamorphics, and comprises up to 1800 m of coarse, immature sandstone and conglomerate. The Westmoreland Conglomerate is divided into five fining-upward sequences deposited in a braided river/alluvial fan environment. The main source of sediments was located in the northeast; the sediment-bearing rivers originated in the rising highlands of the northward extension of the Mt Isa Orogen. Their course was controlled by two east-trending palaeohighs, separated by about 20 km of lowlands. The southern high is represented by the Murphy Inlier and the northern high by a belt of east-trending gravity lows interpreted as granitic basement.