Molesworth is the source of the Clarence, Wairau and Acheron Rivers.
A history of glaciation can be read in the landscape of terminal and lateral moraines, glacial outwash plains, hanging valleys and waterfalls, cirque basins, tarns and arêtes.
Several major active faultlines transect the property causing mountain uplift and more recently triggering landslides and rockfalls.
Altitude ranges from 549 metres to over 2100 metres.
Vegetation reflects the east to west rainfall gradient. At the dry end of the scale, you will see gravelfield and scree communities as well as shrublands. Short tussocklands grow on valley floors and lower mountain side-slopes and tall tussocklands on mountain slopes and in upper parts of catchments.
In wetter country, patches of red tussocks and remnants of mountain beech forest can be found. Manuka and kanuka shrubland communities have in some areas risen from the ashes of burned beech, and are nursing regenerating forests.
Lakes, wetlands and kettlehole bogs provide a treasure trove of moisture-loving plants.
A Protected Natural Areas Programme (PNAP) survey of the reserve in 1987/88 identified 25 recommended areas for protection (RAPs), totalling nearly 30% of the Farm Park's total area. Progress is being made on fencing and protecting these sites.
Molesworth supports one of New Zealand’s most diverse lizard faunas. The nationally threatened scree skink and spotted skink are found here as well as more common species.
Nationally threatened bird species which occur on Molesworth include the southern crested grebe, black-fronted tern, kea, New Zealand falcon, yellow-crowned kakariki, New Zealand pied oystercatcher and banded dotterel.
Molesworth provides valuable habitat, especially during the summer, when most birds leave coastal areas to breed on braided riverbeds. A significant proportion of the national population of black-fronted terns breed in the Wairau, Awatere and Clarence catchments, of which Molesworth forms a part.
Molesworth also provides bird habitat in the shrublands that support high populations of tomtits, robins, rifleman and brown creeper.
Land-locked native fish species, including members of the bully and galaxiid families, occur in lakes and tarns, some unique to Marlborough. Rivers and streams are populated by native fish species and trout.
Several species of spectacularly large giant wetas and speargrass weevils can be found in the area.
Molesworth endures a continental climate of extremes. Hot and generally dry summers are followed by harsh winters. Snow may fall at any time of the year, sometimes covering the entire property for up to eight weeks in the winter.
Average annual rainfall ranges from 670 mm in the east to 3000 mm in the west, the marked gradient reflected in the varied soils and vegetation. Ground frosts occur at the homestead roughly two days in three.