"Creations in Stone: Petroforms in East-River South Dakota" https://www.sdhspress.com/journal/south-dakota-history-35-4/creations-in-stone-petroforms-in-east-river-south-dakotahttps://www.sdhspress.com/@@site-logo/sdshp-logo.jpg
"Creations in Stone: Petroforms in East-River South Dakota"