There are two challenging rides over the isolated back-country hills between Omarama and St Bathans. Both are on rough four wheel drive tracks with lots of river crossings and an altitude gain and then loss of about 600 metres (2000 feet). It's all open tussock country with rugged valleys and high rolling hills. The Hawkdun Range is to the east and the Saint Bathans Range to the West. The panoramas are stunning.
Both tracks start and finish together - the end of Broken Hut Road from Omarma and the top of Hawkdun Runs Road from Saint Bathans. In DOC's "Oteake Conservation Park" brochure they are called the West Manuherikia Track and the East Manuherikia Track.
The West Manuherikia Track is 25km long and the East Manuherikia Track is 19km long. You could ride them both in a loop from either end (if you're very fit and strong). You could also split the loop over two days by spending night in one of the two back country huts on the West Manuherikia Track. If you can organise a shuttle, the easiest option would be to ride the East Manuherikia Track from south to north, ie, from the Saint Bathans end. Another option from either end is ride up to one of the saddles, then go back the way you came.
It's a good idea to wear woollen sox and take some chain oil. These 4wd tracks get steep in places and you can expect to do some pushing. Don't plan this adventure ride after rain or during snow melt as the river crossings are challenging enough, even when low.