  We have recently obtained deep near-IR Keck imaging of a newly-discovered
z=4.04 galaxy (Frye & Broadhurst 1998). This is lensed by the rich foreground
cluster Abell 2390 (z=0.23) into highly-magnified arcs 3-5" in length. Our H-
and K'-band Keck/NIRC imaging allows us to map the Balmer+4000Ang break
amplitude. In combination with high-quality archival HST/WFPC2 data, we can
spatially resolve stellar populations along the arcs. The WFPC2 images clearly
reveal several bright knots, which may correspond to sites of active star
formation. Indeed, in some spatial regions the Keck/LRIS discovery spectra are
consistent with OB-star spectral energy distributions in the rest-ultraviolet.
However, there are considerable portions of the arcs which appear redder with
no Ly-alpha emission, consistent with being post-starburst regions.
