  Overdensities in the radial phase space $(r,v_r)$ of the Milky Way's halo
have previously been associated with the phase-mixed debris of a highly radial
merger event, such as Gaia Sausage-Enceladus. We present and test an
alternative theory in which the overdense 'chevrons' are instead composed of
stars trapped in resonances with the Galactic bar. We develop an analytic model
of resonant orbits in the isochrone potential, and complement this with a test
particle simulation of a stellar halo in a realistic barred Milky Way
potential. These models are used to predict the appearance of action space
$(J_\phi,J_r)$ and radial phase space in the Solar neighbourhood. They are able
to reproduce almost all salient features of the observed chevrons. In
particular, both the analytic model and simulation predict that the chevrons
are more prominent at $v_r<0$ when viewed near the Sun, as is observed by Gaia.
This is inconsistent with formation by an ancient merger event. We also
associate individual chevrons with specific resonances. At a bar pattern speed
of $\Omega_\mathrm{b}=35$ km s$^{-1}$kpc$^{-1}$, the two most prominent
prograde chevrons align very closely with the corotation and outer Lindblad
resonances. The former can be viewed as a highly eccentric extension of the
Hercules stream. Finally, our model predicts that the $v_r$ asymmetry changes
sign as a function of Galactic radius and azimuth, and we find evidence that
this is indeed the case in the Milky Way.
