  Inelastic dark matter with moderate splittings, $\mathcal{O}({\rm few} \;
{\rm to} \; 150)$ keV, can upscatter to an excited state in the Earth, with the
excited state subsequently decaying, leaving a distinctive monoenergetic photon
signal in large underground detectors. The photon signal can exhibit
sidereal-daily modulation, providing excellent separation from backgrounds.
Using a detailed numerical simulation, we examine this process as a search
strategy for magnetic inelastic dark matter with the dark matter mass near the
weak scale, where the upscatter to the excited state and decay proceed through
the same magnetic dipole transition operator. At lower inelastic splittings,
the scattering is dominated by moderate mass elements in the Earth with high
spin, especially $^{27}$Al, while at larger splittings, $^{56}$Fe becomes the
dominant target. We show that the proposed large volume gaseous detector CYGNUS
will have excellent sensitivity to this signal. Xenon detectors also provide
excellent sensitivity through the inelastic nuclear recoil signal, and if a
future signal is seen, we show that the synergy among both types of detection
can provide strong evidence for magnetic inelastic dark matter. In the course
we have calculated nuclear response functions for elements relevant for
scattering in the Earth, which are publicly available on GitHub.
