Britannica AI Icon
Adding us as a Preferred Source tells Google you trust our content, so our articles show up more often in your Google Search, Discover feed, and AI Overviews.
verifiedCite
While every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions.
Select Citation Style
Feedback
Corrections? Updates? Omissions? Let us know if you have suggestions to improve this article (requires login).
Thank you for your feedback

Our editors will review what you’ve submitted and determine whether to revise the article.

External Websites

tufa cave, umbrella-like canopy formed as a calcium-carbonate-saturated stream plunges over a cliff. As the water is aerated, carbon dioxide is released, causing the calcium carbonate to be deposited. Tufa caves may completely bridge a river, forming a natural tunnel. One of the largest such caves is Tonto Natural Bridge near Payson, Ariz.