The Rinconada fault near Santa Margarita is a major northwest-trending, high-angle fault that separates a terrane of granitic basement on the northeast from one of Franciscan basement on the southwest. Southeastward from Santa Margarita this fault extends continuously into the "Nacimiento" fault across Cuyama Gorge to intersect the Big Pine fault in the San Rafael Mountains. Northwestward the Rinconada fault does not extend into the Nacimiento fault near the Nacimiento River, as presumed, but veers northward through Paso Robles into a line of faults locally called San Marcos, Jolon, and Espinosa faults, nearly to Reliz Canyon west of King City.

Detailed mapping reveals that all these aligned faults are parts of one major fault, 160 mi long. Therefore, it is proposed to call it the Rinconada fault. It is separated by a 2-mi gap from the Reliz fault, aligned northwest along the base of Sierra de Salinas. The Rinconada fault, as defined herein, is nearly parallel with, and about 22 mi southwest, of the San Andreas fault. Southeastward from Santa Margarita the Rinconada fault is along the southwestern border of the Salinia block; northwestward from that town it extends into this block. Drag folding along and near the Rinconada fault indicates right-lateral movement. Much of this movement occurred before deposition of the Paso Robles Formation. Strata of Miocene and early Pliocene ages are offset about 11 mi near Paso Robles; tho e of Late Cretaceous-early Tertiary age are offset nearly 40 mi.

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