This investigation focuses on syllable boundary demarcation in Hualapai and Havasupai, both native American Indian languages spoken in Northern Arizona. In an attempt to understand better the nature of the syllable, allophonic variation with respect to syllable position is examined. Cross-linguistic evidence suggests that sounds may take on similar characteristics according to their position in the syllable. I. Maddieson (1985) found phonetic vowel shortening before geminates in languages as diverse as Kannada, Hausa, Finnish, and Italian. Phonetic vowel shortening in closed syllables was also found in Havasupai. A relationship between lexical stress and allophonic variation inside the syllable was found in Hualapai and Havasupai. Vowel lowering in closed syllables was also found in Hualapai and Havasupai. (Author)