Cairn Hills

The Cairn Hills are generally regarded as a northern spur of the Abbor-Alz, stretching north to the Nyr Dyv (as is obvious). Their character becomes increasingly differentiated from the Abbor Alz the farther north one travels, becoming less sharply undulating and lower. The hills are granitic and contain large quartz deposits and important resources, although the surface soil is usually shallow and of poor fertility.
The northernmost promontory of the hills, beyond the mouth of the Selintan, yields fine gems, especially rubies and emeralds and a few diamonds. The Free City is happy to allow the gnomes of Grossettgrottell and the outlying smaller mines exclusive control over mining them, given gnomish skills. The gnomes prize this, and protect their terrain jealously.
As one travels east along the Midbay of the Nyr Dyv, these gem deposits rapidly diminish and the hills here have poor mineral wealth; farther south, jade and amethyst can be found. However, in this area are found many of the legendary burial sites which give the Cairn Hills their name. These are the ancient treasure graves that provided such a vital source of revenue in Greyhawk’s wild, early days before trade brought the coffers of the city its present largesse.
The large majority of these cairns were plundered of their wealth long ago; as places for adventure, They were surpassingly dangerous and strange. The cairns were of many types, some so alien that sages mutter about people from other worlds creating them; some are pyramidal, others polyhedral and complex in design. Others were simpler, little more than barrow mounds.
From these cairns, famed and fabled adventurers of legend pillaged great wealth and unique magics. Great ingots of precious metal, rare super hard steels, planar tomes and traveling devices, and much else were brought back to the Free City, together with tales of hideous deaths and monstrous guardians. The treasures were as sought after as the origins of the cairns were unknown, surely earlier than recorded Oerth history.