  We present high spatial resolution observations of the continuum emission
from the young multiple star system UZ Tau at frequencies from 6 to 340 GHz. To
quantify the spatial variation of dust emission in the UZ Tau E circumbinary
disk, the observed interferometric visibilities are modeled with a simple
parametric prescription for the radial surface brightnesses at each frequency.
We find evidence that the spectrum steepens with radius in the disk, manifested
as a positive correlation between the observing frequency and the radius that
encircles a fixed fraction of the emission ($R_{eff} \propto \nu^{0.34 \pm
0.08}$). The origins of this size--frequency relation are explored in the
context of a theoretical framework for the growth and migration of disk solids.
While that framework can reproduce a similar size--frequency relation, it
predicts a steeper spectrum than is observed. Moreover, it comes closest to
matching the data only on timescales much shorter ($\le 1$ Myr) than the
putative UZ Tau age (~2-3 Myr). These discrepancies are the direct consequences
of the rapid radial drift rates predicted by models of dust evolution in a
smooth gas disk. One way to mitigate that efficiency problem is to invoke
small-scale gas pressure modulations that locally concentrate drifting solids.
If such particle traps reach high continuum optical depths at 30-340 GHz with a
~30-60% filling fraction in the inner disk ($r \lesssim20$ au), they can also
explain the observed spatial gradient in the UZ Tau E disk spectrum.
