  Twisted bilayer graphene (tBLG) has recently emerged as a platform for
hosting correlated phenomena, owing to the exceptionally flat band dispersion
that results near interlayer twist angle $\theta\approx1.1^\circ$. At low
temperature a variety of phases are observed that appear to be driven by
electron interactions including insulating states, superconductivity, and
magnetism. Electrical transport in the high temperature regime has received
less attention but is also highly anomalous, exhibiting gigantic resistance
enhancement and non-monotonic temperature dependence. Here we report on the
evolution of the scattering mechanisms in tBLG over a wide range of temperature
and for twist angle varying from 0.75$^\circ$ - 2$^\circ$. We find that the
resistivity, $\rho$, exhibits three distinct phenomenological regimes as a
function of temperature, $T$. At low $T$ the response is dominated by
correlation and disorder physics; at high $T$ by thermal activation to higher
moir\'e subbands; and at intermediate temperatures $\rho$ varies linearly with
$T$. The $T$-linear response is much larger than in monolayer graphenefor all
measured twist angles, and increases by more than three orders of magnitude for
$\theta$ near the flat-band condition. Our results point to the dominant role
of electron-phonon scattering in twisted layer systems, with possible
implications for the origin of the observed superconductivity.
