When we first heard about this we were amazed there was no Earth Cache located here. After our trip to the South Island at the end of December 2010, we decided to look into the geography, geology and history of the Clay Cliffs. 
Interestingly enough there are 1000's of pictures on the net but vey little information about their formation, much of which you require more than a PhD in geology to understand. The point of this earth cache is teach you a little bit about them and for those with a PhD in geology there is a more detailed section below for your viewing pleasure.
Essentially there is a fault called the Ostler Fault which runs through the region and the cliffs are the result of natural erosion created by this fault
Slightly more scientifically : The Hawkdun Group sediments, uplifted and tilted by the Ostler Fault Zone, form the Clay Cliffs near Omarama. The pale grey material near the base has more quartz and less lithic gravel than the darker material overlying it.
Now for those with a PhD here is the really scientific detail:
Late Miocene tectonic uplift of Central Otago ranges and reworking of quartzose cover sediments gave rise to the coarsening-upward, sandstone and conglomerate dominated Hawkdun Group, which is widespread in the Maniololo basin and in the Waitaki valley from Clay Cliffs to Kurow.
The name Hawkdun Group was prompsed for the late Miocene-Pliocene succession of tectonically generated sediments in the Maniototo, Ida, and Manuherikia Basins, and the name Maniototo Conglomerate was proposed to replace Maori Bottom. The Hawkdun Group in Central Otago can be subdivided into two mappable units. The basal Wedderburn Formation consists predominantly of late Miocene quartzose fluvial strata recycled largely from cover strata of the St Bathans, Kakanui, and Hawkdun Ranges. Wedderburn Formation contains an upwardly increasing component of first-cycle lithic detritus derived from these ranges, and grades up into late Miocene-Pliocene Maniototo Conglomerate, consisting of thick beds of greywacke-dominated conglomerate and interbedded loess horizons. In previous usage, Wedderburn Formation included some strata which more appropriately belong with the underlying Manuherikia Group.
The basal Wedderburn Formation is quartz-lithic sandstone and conglomarate. Overlying Maniotolo Conglomerate is composed of well rounded, imbricated clasts of Rakaia terrane sandstone with some schist. Clasts and matrix are generally weathered to a rusty red-brown colour, although in reducing environments the conglomerate may be bluegrey.
In places the Hawkdun Group is imerfingered with upper pans of the generally underlying Manuherikia Group. Both confonnable and unconfonnable contacts are known, with the latter tending to be near tectonically deformed range fronts, where Hawkdun Group sediments characteristically dip steeply.
Now for the logging requirements...
In order to log the cache you will need to do the following:
1) Go to S44 29.369 E169 52.157 where you will find a sign. Please email us the two words that are written in RED on the sign.
2a) Go to the listed co-ords for the cach and email us the altitude at this point.
2b) Estimate the height of the cliffs (the tallest peak you can see).. There are a number of ways to do this - One would be to note the angle of the sun and the length of the shadows and using some basic geometry you should be able to determine their heights. PLEASE DO NOT ATTEMPT TO CLIMB THE CLIFF FACE to get an Upper Reading !
3) Upload a photo of you and your GPS near the given cache co-ordinates (Optional).
PLEASE NOTE: The cliffs are on private land and there is a small entrance fee to cross the private land ($5 in the form of an honesty box located at Waypoint mentioned below). You will also need to travel on Sand Roads for about 10kms.