Brooke and Orion on the summit of Wildcat Peak in Deem Hills July 2006 From the lofty summit of Deem Hills, at 2100 feet above sea level, and 600 feet above the valley floor, you can get a beautiful 360-degree view of the landscape. Like many of the surrounding desert peaks, Deem Hills is made of rubble leftover from volcanic eruptions that occurred between two and five million years ago, which is relatively recent by geologic standards. The dark rocks, called basalt, glow deep purple and orange in the evening sun. Basalt is basically cooled off lava. Here, many of the rocks have pits and holes in them, evidence that the lava was almost frothy when it flowed and then quickly cooled, leaving small air bubbles in the rock.
According to archeologists in the Phoenix area, rocks found on Deem Hills were prized by native peoples for hundreds of years. Both the basalt and a white rock called chalcedony (pronounced “kal-sed-nee”) were used for many types of tools by prehistoric cultures. The basalt is especially useful to make manos and metates, which are stones commonly used for grinding mesquite pods and grains into flour. Basalt can also be shaped into hammers and axes.
On the south face of the hills there is a thin band of chalcedony, which is a fine-grained quartz that can be shaped into arrowheads, knives and scrapers. An ancient quarry just below the east ridge of Deem Hills was a primary source for people throughout the region who migrated along the Skunk Creek corridor. Because the quality of chalcedony in the Deem Hills is very good, rocks were probably traded for many miles from the source. Some contemporary Native Americans teach that chalcedony is a sacred stone, and is said to augment emotional balance, vitality, stamina, endurance, kindness, charity and friendliness. Another interesting rock phenomenon in the area are the smooth and translucent white nodules of calcite that have eroded out of the outcrops of chalcedony. The nodules are usually about half an inch in diameter, and are common along all of the trails in Deem Hills. I call them "desert pearls." These would make pretty beads for someone who is feeling creative!
For more information about the local geology and archaeology, visit the Deer Valley Rock Art Center at 3711 West Deer Valley Road, below the Adobe Dam just 2 miles south of Deem Hills.
Since May 2005, I have written a natural history column for a neighborhood newsletter published by Jennifer Moore called "Our Big Backyard: Natural History of the Deem Hills," and since 2010, "A Suburban Naturalist."All of these columns are reproduced here. Deem Hills is a City of Phoenix Desert Preserve located just north of Happy Valley Road in north central Phoenix, and just west of I-17. The Preserve and adjacent hills comprise over 900 acres of open space with several miles of hiking trails. For more perspectives from the Deem Hills and suburban Phoenix, also check out my companion blog, Kat Tracks.
As a naturalist with a special interest in botany and plant ecology, some of my greatest passions are to explore, photograph and write about native plants. If I can spark an awareness or interest in natural history in others along the way, that is my greatest reward.