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Cryptoendolithic habitats in the Canadian high Arctic are host to a diverse assemblage of microorganisms including cyanobacteria, algae, fungi and heterotrophic bacteria. Communities grow as biofilms attached to mineral surfaces as well as within the open void spaces between grains and in many cases produce extracellular polysaccharides in response to the extreme environmental conditions. In situ observations of the cryptoendolithic habitat as well as ultrastructural examination of microorganisms show that this EPS provides a substrate for accumulation of allochthonous clay particles that enter the system by winds and rain. The lack of evidence for biomineralization within this habitat contrasts with similar environments in the Antarctic Dry Valleys, a consequence of warmer temperatures and wetter conditions that increase erosion rates and subsequent habitat destruction, effectively limiting the time possible for biomineralization by living microorganisms as well as the formation of biosignatures or microfossils.