Over the period from 1955 until 1976 an outcrop of Ordovician porphyritic rhyolite was quarried for road-sealing aggregate and rail ballast from two quarries at Mount Monster, 12 km south of Keith. The total recorded production was 548,000 tonnes. Recently, Mineral Claim 3631 has been pegged over the larger northern quarry, on Section 499, Hundred of Stirling (Water and Stone Reserve No. 1). The smaller quarry, 150 m to the south, is covered by Private Mine 173. PM 173 also covers and pre-dates part of the Mount Monster Conservation Park lying to the south. At its formation, this Park was proclaimed as a single proclamation park (i.e. with management jurisdiction vested solely in the State Department of Environment and Heritage - DEH). Plans being made to resume quarrying at both quarries are considered as contentious due to their proximity to the Park, plans by the DEH to incorporate both sites into the Park, the presence of native vegetation including threatened species, and some local opposition to any resumption of quarrying. The authors' assessment of the information previously compiled for this resource occurrence, including material testing data, confirms that the Mount Monster quarry sites have excellent geological potential to supply high quality aggregate for the upper South-East region. Their investigations of nearby similar type outcropping igneous rock bodies that might possibly be available as alternative quarrying sites, made using existing regional geological mapping data and field inspections, suggest that the fine-grained volcanic rocks at Mount Monster and Papineau Rocks are by far the best potential aggregate sources in the region, having very good durability and skid resistance properties. However, the Papineau Rocks outcrop is much less suitably located to supply the Bordertown-Keith-Tailem Bend region, being about 80 km by road south of Mount Monster. Ordovician granite outcrops are relatively common in the region, but their coarse-grained nature makes them unsuitable for use as road-sealing aggregates. Resources at the Mount Monster northern quarry site are estimated at 600,000 tonnes, or 1,000,000 tonnes for a deeper final quarry design. Resources for a larger development incorporating the southern quarry have not been estimated, but are likely to be considerably larger. Overburden depths between the existing quarries would need to be established in order to estimate the latter.