  Studying the stellar populations in the outskirts of spiral galaxies can
provide important constraints on their structure, formation, and evolution. To
that end, we present VI photometry obtained with the Advanced Camera for
Surveys for three fields located ~ 20' - 30' in projected distance southeast of
M33's nucleus (corresponding to ~ 4 - 6 visual scale lengths or ~ 9 - 13 kpc in
deprojected radius). The color-magnitude diagrams reveal a mixed stellar
population whose youngest constituents have ages no greater than ~ 100 Myr and
whose oldest members have ages of at least several Gyr. The presence of stars
as massive as 3 - 5 Msun is consistent with global star formation thresholds in
disk galaxies but could argue for a threshold in M33 that is on the low end of
observational and theoretical expectations. The metallicity gradient as
inferred by comparing the observed red giant branch (RGB) to the Galactic
globular clusters is consistent with M33's inner disk gradient traced by
several other studies. The surface density of RGB stars drops off exponentially
with a radial scale length of 4.7' +/- 0.1'. The scale length increases with
age in a manner similar to the vertical scale height of several nearby
late-type spirals. Based on the metallicity gradient, density gradient, and
mixed nature of the stellar populations, we conclude these fields are dominated
by a disk population although we cannot rule out the presence of a small halo
component.
