Endangered Hausa dialects spoken in Jigawa State and selected communities in Kano, Katsina, and Yobe States represent an irreplaceable repository of cultural and linguistic heritage, yet these varieties are diminishing at an accelerating rate under the pressure of urbanisation, formal education in Standard Hausa, and mass media. This paper reports the principal findings of a linguistic documentation project that conducted the first systematic digital preservation of nine endangered Hausa dialect varieties across the four-state study region. Using a linguistic documentation research design, the project engaged 120 native speaker participants distributed across three age cohorts and nine dialect communities. Data were collected through 84 hours of audio and video recording, semi-structured interviews, participant observation, GPS-based dialect mapping, and systematic metadata documentation. Linguistic analysis produced annotated transcriptions of all recordings, a lexical database of 1,850 entries including 342 dialect-only lexical items, a phonological description of 24 unique tone contrasts and 18 distinct vowel patterns, 216 documented proverbs, and 68 dialect-specific kinship terms. A digital archive of 120 gigabytes was created following UNESCO and Endangered Language Documentation Programme standards. Language vitality assessment using the UNESCO framework revealed that six of the nine documented varieties score at or below the 3.0 endangered threshold, with Guri dialect critically endangered at 2.1. Mean young adult dialect use rates average 36 percent of elderly speaker rates, confirming severe intergenerational transmission failure. The study proposes a three-phase Digital Preservation Framework and offers evidence-based recommendations for language policy, curriculum design, and institutional capacity building in Nigerian Hausa dialect documentation.