Geological heritage is insufficiently recognised in Australia; it should be considered in its own right, not as an addendum to other heritage values. The lack of a suitable robust and repeatable methodology has seriously constrained the assessment of geological sites suitable for the National Heritage List (NHL). A desktop assessment of Australian desert landscapes required intrinsic natural values of a diverse group of sites, spread over a vast area, to be assessed against NHL criteria. The Earth Sciences Comparative Matrix (ESCoM) was developed for this study. In the ESCoM, sites are grouped in process themes. Each is assessed against NHL criteria then compared with other similar places, according to degree of unusualness, integrity, and authenticity. A site scoring well across multiple themes has increased heritage significance. The overall values of a site are quantified, leading to a qualitative judgement on whether it achieves the threshold of outstanding heritage value. Examples of assessment using this method are given. In this methodology, significance determination is based on rigorous comparisons of specific values. It is semi‐quantitative, repeatable, and robust. It differs from other geoheritage assessment methods in its combination of process‐based groupings (facilitating the separation of site type from heritage criteria), matrix structure (minimising complexities of scale or diversity), and use of numerical rankings as an aid in decision‐making. While the study for which ESCoM was developed was focused on landforms, it can be used for other types of geoheritage (e.g. fossils, tectonic processes), with modification of matrix theme headings.