"Very 'shallow' and clear river, and even on a cloudy day a Mammoth Tusk is easily spotted...in the river gravel, this particular 'Cow Tusk' Mammoth was in very excellent shape as far as the quality of the ivory...but at some point in it's history, it had been broken.  This is common for some tusks, as the tusk, when first exposed by erosion in the river bank, still remains partially frozen in the permafrost.  As 'Spring Breakup' the huge ice flows rushing downriver can intercept the tusk and 'snap' it off leaving part of the tusk remaining in the frozen wall of ice."