This paper focuses on tonal development in Baima, a little-studied Tibetic (Tibeto-Burman) language of China. Based on newly collected data and an updated phonological analysis, it addresses the phonetic and chronological challenges posited by the previous analysis of tonal developments in Baima by Huang & Zhang (1995). As suggested by historical-comparative evidence (correspondences between Baima and Written Tibetan), the three contrastive tonal categories in Baima have likely arisen through an overlay of the phonation difference in consonants (historically breathy vs. non-breathy) and the phonation difference in vowels (tense vs. lax, with pitch and vowel duration as co-articulated cues). I furthermore argue that the development of a tense/lax distinction is likely broadly shared by the Tibetic languages neighboring Baima. Recognition of such a multidimensional contrast (which may variously implicate differences in phonation, pitch, vowel duration, and vowel quality) provides a unified explanation for a number of seemingly unrelated and unusual characteristics of these Tibetic languages (such as rhyme length and onset aspiration as pathways leading to distinctive low register). The clustering of Tibetic languages with a tense/lax distinction in the historically multilingual area at the border of the present-day Northern Sichuan and Southern Gansu is further brought in connection with local non-Tibetic languages, some of which possibly share a structurally similar voice quality contrast that involves sets of correlated phonetic properties associated with phonatory, tonal, and vowel quality.