Figure 3.  Stratigraphy of the Pit, one of the best-studied fossil localities in Porcupine Cave. Magnetostratigraphy of these sediments was interpreted to include the Brunhes-Matuyama boundary. Reproduced with permission from A.D. Barnosky, ed., Biodiversity Response to Climate Change in the Middle Pleistocene: The Porcupine Cave Fauna from Colorado, © 2004 by The Regents of the University of California.