In the complex two-dimensional parameter space of quadratic rational maps, it is of interest to study dynamically defined one-dimensional slices. An interesting collection of such slices are the curves formed by maps having a periodic critical point, of a given period. We obtain a formula for the Euler Characteristic of these curves. The formula is an application of the study of degenerate holomorphic families of quadratic rational maps with tools from non-Archimedean dynamics.