  We present Spitzer IRAC images that indicate the presence of cavities cut
into the dense outer envelope surrounding very young pre-main sequence stars.
These young stellar objects (YSOs) characterized by an outflow represent the
earliest stages of star formation. Mid-infrared photons thermally created by
the central protostar/disk are scattered by dust particles within the outflow
cavity itself into the line of sight. We observed this scattered light from 27
nearby, cavity-resolved YSOs, and quantified the shape of the outflow cavities.
Using the grid models of Robitaille et al. (2006), we matched model spectral
energy distributions (SEDs) to the observed SEDs of the 27 cataloged YSOs using
photometry from IRAC, MIPS, and IRAS. This allows for the estimation of
geometric and physical properties such as inclination angle, cavity density,
and accretion rate. By using the relative parameter estimates determined by the
models, we are able to deduce an evolutionary picture for outflows. Our work
supports the concept that cavities widen with time, beginning as a thin
jet-like outflow that widens to reveal the central protostar and disk until the
protostellar envelope is completely dispersed by outflow and accretion.
