Since the seminal work of Pike (1944, 1948), a long tradition of documentation of Mixtec tonal systems has revealed the complexity and diversity of these systems. Much of this work has also been accompanied by efforts in language sustainability. However, many Mixtec varieties remain undocumented and most previous work has focused on lexical tone, with interactions between lexical and grammatical tone being relatively understudied in comparison. This paper offers the first comprehensive investigation of the tone patterns found in the previously undocumented San Juan Piñas variety of Mixtec (Tò'ōn Ndá'ví), focusing on interactions between lexical and grammatical tone. This paper shows that (i) the association of grammatical tone is determined by the (under)specification of individual Tone-Bearing-Units in verb stems, and that (ii) some grammatical tones may exhibit non-local association in a tonally defined class of verbs. This paper concludes by discussing the implications of these findings for an ongoing development of an orthographic convention for SJPM, as part of a larger language reclamation effort led by co-author Claudia Juárez Chávez.