B.C. or A.D. refer to 'Before Christ' and 'Anno Domini' (Latin for 'year of our Lord' respectively. These designations are used to measure chronological time and demonstrate to what extent religion still plays a role in the construction of of contemporary concepts of historical time. Another way to conceive of current time and history is to use a geological framework. According to the United States Geological Survey, the Los Angeles basin is currently in the Holocene Epoch, of the Quaternary Period in the Cenozoic Era, of the Phanerozoic Eon. The Holocene Epoch began after the retreat of the last great glacial period, about 15,000 years ago.
petroglyph: petroglyphs are also known as Indian writing, picture writing, and rock art. They include paintings, carvings, and other forms.