Ultima is a town and district in northern Victoria, Australia. The town is in the Rural City of Swan Hill local government area, north-west of the state capital, Melbourne and south-west of Swan Hill. At the 2021 Census Ultima had a population of 173, down from 333 in 2011.
Locality
The district of Ultima is bounded to the north by Waitchie Rd which joins the Sea Lake-Swan Hill Road near the 14 Mile Bushland Reserve to the east. The eastern border extends south along Ceveri Road, west along Lake Boga-Ulitma Road, south again along Dog Netting Fence Road to join the southern boundary at Stumpy Lane and crossing the South Meatian Channel. At the junction of Stumpy Lane and Grey Road, the eastern boundary extends southwards again, crossing Rees Channel. The southernmost boundary extends westwards from the intersection of Grey Road with Meatian West Road, across Murnungin Channel at two points. Meatian West Road and Hancock Road junction makes the south-western corner of the Ultima district. Hancock Road heading north crosses Culgoa-Ultima Road to become Ford Road which meets Burns Road, and that extends a boundary westward, across another branch of Murnungin Channel to Loader Road which forms the northern end of the western boundary to Waitchie Road.
Geology
See main article Murray Basin
Ultima is situated in the Murray Basin, formed after Australia separated from Antarctica. The oldest rocks identified in the region are Cambrian era ocean floor basalts distributed along major faults, particularly the Governor (aligned with the Murray River), Log Landing, and Griminal faults. The southern and western areas are covered by the Cambrian St Arnaud Group and the Ordovician Castlemaine Group, formations which were likely deformed during the Benambran Orogeny, followed by a significant period of granite intrusion. The Lalbert Batholith, south of Ultima exhibits an unusual magnetic pattern which may have resulted from dextral strain on the granites while they were still in a plastic state; an event that is one of the few Bindian occurrences recorded in western Victoria.
The Kanimblan Orogeny appears to have only impacted the southern part of the Governor Fault system, as well as the Lake Charm and associated faults. Limited direct evidence of further sedimentation appears in the Swan Hill region until the Cainozoic era, though Permian sediments from the Numurkah Trough centred 200km east along the Murray, might be present, particularly in the eastern area. Around 120 basaltic plugs were intruded, but the surface deposits associated with these were likely eroded, contributing to the detritus of the Late Jurassic to Early Cretaceous Otway Group.
In more recent times, from the Eocene to the present, the riverine plains of the Murray Basin have been extensively covered by sediments. These sediments can be classified into four sequences. The oldest is the Eocene to Oligocene Olney Formation of the Renmark Group, which is predominantly fluvial and contains abundant plant material. It is overlaid by the Mologa Surface, which might record a period of monsoonal weather patterns. Above this is the Oligocene to Miocene Murray Group, which includes the fluvial Calivil Formation and the marginal marine Geera Clay. Further up are the Late Miocene to Pliocene Bookpurnong beds, Parilla Sand, and Shepparton Formation time equivalents, representing offshore marginal marine and onshore facies. All of these formations are below the Karoonda Surface. The present cycle consists of fluvial (Coonambidgal Formation), lacustrine (Blanchetown Clay and unnamed lunettes), and windblown sand (Woorinen Formation, Lowan Sand). The region also contains both sheet and strand line style heavy mineral deposits, with one strand line deposit having been mined at Wemen, 110 km to the north of Ultima Traces of uranium are known in the Lake Boga Granite, and there might be additional occurrences around Lake Tyrrell.