Given the historic precedent of the 1857 earthquake and its
foreshocks, a deficit of slip of more than 4 m accumulated since 1857,
and a major gap in paleoseismic sites northwest of their concentration
in the Carrizo Plain, Arrowsmith and M.S. student Elizabeth Zima and Ph.D. student Jeri Young
focused on the southern 15 km of the Cholame segment and
developed a paleoseismic site called LY4 (Fig. 2). Arrowsmith, Stone,
and colleagues originally mapped the recently active faults and
tectonic geomorphology along that reach to identify LY4 (see below
for more discussion of this mapping). The mapping results were
reported in Stone (1999), while the paleoseismic results are in Stone
et al. (2002) and Young et al. (2002). Evidence for at least three earthquakes since about 1030 A.D. including the 1857 event, and 3±
0.5 m of slip in 1857 across a 5 m aperture was exposed in the
numerous excavations at LY4.