  We present optical spectroscopy of 710 solar neighborhood stars collected
over twenty years to catalog chromospheric activity and search for stellar
activity cycles. The California Legacy Survey stars are amenable to exoplanet
detection using precise radial velocities, and we present their Ca II H and K
time series as a proxy for stellar and chromospheric activity. Using the HIRES
spectrometer at Keck Observatory, we measured stellar flux in the cores of the
Ca II H and K lines to determine S-values on the Mt. Wilson scale and the
log(R'HK) metric, which is comparable across a wide range of spectral types.
From the 710 stars, with 52,372 observations, 285 stars are sufficiently
sampled to search for stellar activity cycles with periods of 2-25 years, and
138 stars show stellar cycles of varying length and amplitude. S-values can be
used to mitigate stellar activity in the detection and characterization of
exoplanets. We use them to probe stellar dynamos and to place the Sun's
magnetic activity into context among solar neighborhood stars. Using precise
stellar parameters and time-averaged activity measurements, we find tightly
constrained cycle periods as a function of stellar temperature between
log(R'HK) of -4.7 and -4.9, a range of activity in which nearly every star has
a periodic cycle. These observations present the largest sample of
spectroscopically determined stellar activity cycles to date.
