  We use the Fourth Data Release of the Sloan Digital Sky Survey to test the
ubiquity of infall patterns around galaxy clusters and measure cluster mass
profiles to large radii. We match X-ray cluster catalogs with SDSS, search for
infall patterns, and compute mass profiles for a complete sample of X-ray
selected clusters. Very clean infall patterns are apparent in most of the
clusters, with the fraction decreasing with increasing redshift due to
shallower sampling. All 72 clusters in a well-defined sample limited by
redshift (ensuring good sampling) and X-ray flux (excluding superpositions)
show infall patterns sufficient to apply the caustic technique. This sample is
by far the largest sample of cluster mass profiles extending to large radii to
date. Similar to CAIRNS, cluster infall patterns are better defined in
observations than in simulations. Further work is needed to determine the
source of this difference. We use the infall patterns to compute mass profiles
for 72 clusters and compare them to model profiles. Cluster scaling relations
using caustic masses agree well with those using X-ray or virial mass
estimates, confirming the reliability of the caustic technique. We confirm the
conclusion of CAIRNS that cluster infall regions are well fit by NFW and
Hernquist profiles and poorly fit by singular isothermal spheres. This much
larger sample enables new comparisons of cluster properties with those in
simulations. The shapes (specifically, NFW concentrations) of the mass profiles
agree well with the predictions of simulations. The mass inside the turnaround
radius is on average 2.19$\pm$0.18 times that within the virial radius. This
ratio agrees well with recent predictions from simulations of the final masses
of dark matter haloes.
