I will present and discuss a plugin for PETSc's PCGAMG (generic algebraic multigrid) preconditioner, called DofColumns. DofColumns is intended for problems that have strong mesh-aligned anisotropy, but for which a geometric multigrid is either inappropriate or unavailable. Such problems occur in climate system modeling, where domains can span thousands of kilometers horizontally but remain O(1) km thick or less. The particular motivating example in this case is ice sheet modeling, where the W:H aspect ratios for discretization are typically 25:1 or greater. DofColumns works by dividing the aggregation phase of restriction construction into horizontal and vertical sub-phases. DofColumns is also intended to be a simple example of the extensibility of the PCGAMG framework for algebraic multigrid, and its use to generate AMG variants tailored to individual problems.