ABSTRACT
Most of the ground-stone tools from Guila Naquitz were made of ignimbrite, or volcanic tuff, from the Miocene volcanics that constitute bedrock in the eastern Valley of Oaxaca. It appears that the occupants of the cave picked up ignimbrite cobbles from stream beds in the Mitla area to use as one-hand manos. They also carried in ignimbrite slabs to use as metates and larger cobbles or small boulders to use as mortars. Thus, rotary action produced both ovoid mullers and basin-shaped milling stones, while back-and-forth motion produced both oblong manos and trough metates. Mortars were probably used with the pestle-like pecked and rounded ends of some one-hand manos, but they might also have been used with some of the pebble hammerstones found at Guila Naquitz. Because these hammerstones were usually made of chert or silicified ignimbrite they have been included with the chipped-stone tools, but the possibility that some were occasionally used with mortars cannot be ruled out.
