  We present a single-source dual atom interferometer and utilize it as a
gradiometer for precise gravitational measurements. The macroscopic separation
between interfering atomic wave packets (as large as 16 cm) reveals the
interplay of recoil effects and gravitational curvature from a nearby Pb source
mass. The gradiometer baseline is set by the laser wavelength and pulse
timings, which can be measured to high precision. Using a long drift time and
large momentum transfer atom optics, the gradiometer reaches a resolution of $3
\times 10^{-9}$ s$^{-2}$ per shot and measures a 1 rad phase shift induced by
the source mass.
