The presence of species disjunct from more northern distributions and quantitative aspects of species associations were studied on the Sierra La Asamblea, an isolated range reaching 1,661 m elevation at about 29.3°N on the Baja California Peninsula. The flora above 800 m is composed of ≥299 species of tracheophytes, notably including Pinus monophylla and Adenostoma fasciculatum. Eighty-seven species are considered disjunct from more northern distributions, of which only 19 have affinity limited to the California Floristic Province. Data from 10 transects and adjacent flora show few species that are either broadly distributed or locally common, and both composition and structure differ from studies at lower elevations. Disjuncts were most common in association with P. monophylla. Range extensions (38) are reported, including three new records for the peninsula, and a floristic list is provided.