The Toonolian Marshes are a large wetland area between Phundahl and Toonol. It is dotted with many islands and filled with eccentric wildlife. Because of the large insects and the many reptile and rodent species that inhabit the marshes, it is extremely dangerous, but this has also made it attractive to Ras Thavas, a brilliant but unsentimental scientist who built his lab deep within the marshes. The marsh is also the site of Gooli, the only known location upon Barsoom that the Kangaroo Men are found.

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