Pennsylvanian to Permian limestone of the Horsefeed Formation Cache Creek Complex outcrops over an extensive area surrounding Talaha Bay on Taku Arm of Tagish Lake.

Talaha Bay lies near the western margin of a belt of limestone with minor mafic flows and lithic tuff, which is at least 12 kilometres wide and extends northwest from Atlin Lake, across Taku Arm of Tagish Lake into the Yukon Territory. The limestone is estimated to be between 900 and 1500 metres thick.

Two distinct carbonate members are distinguished. The most extensive member consists of variably recrystallized, medium- to pale-grey, massive bioclastic limestone of Middle to Upper Pennsylvanian age. This limestone is sometimes contaminated with black, nodular chert. A less extensive, overlying Permian limestone member contains massive, locally thick- to medium-bedded, dark grey to black limestone, that is rarely dolomitic.