Question
What types of rocks and minerals are common in Williams, AZ?
Answer
Williams, Arizona, is on the western-most edge of the San Francisco volcanic field. The rocks exposed near Williams are predominantly basalts with small phenocrysts (minerals) of olivine, pyroxene and plagioclase. You won't find the large olivine (peridot) crystals that are found in the San Carlos volcanic field of central Arizona.
The Bill Williams Mountain volcanic complex comprises a suite of coalescing andesitic to dacitic lava flows and volcanic domes emplaced about 3.5 million years ago on the southwestern edge of the San Francisco volcanic field, east of Flagstaff, Arizona. I don't have in front of me a description of Bill Williams Mtn. rocks, but andesites and dacites typically include: plagioclase feldspar, pyroxene, hornblende, biotite, and quartz.
Photo by Ted Grussing. The town of Williams is left of BWM. On the horizon, from right to left, are four younger volcanic vents: Mount Elden, the San Francisco Peaks (including Humphreys Peak the highest point in Arizona at 12,637’), Kendrick Peak and Sitgreaves Mountain.
Thanks for your question.
Mike
