Selective colleges are sites of social closure. Scholarship examines how selective colleges evaluate applicants, but colleges do not passively accept applications. They recruit. If college recruiting territories are structured by shared infrastructures, then mechanisms of social closure operate upstream of admissions. This article examines how College Board Geomarkets and the Market Segment Model structure high school recruiting visits by selective colleges. Geomarkets carve metropolitan areas into smaller geographic units meant to define local recruiting territories. The Market Segment Model predicts how student demand varies by Geomarket as a function of social class. These market devices became embedded in organizational structures and in third-party products that produce college recruiting behavior. Using data on recruiting visits made in 2017 by 42 selective colleges, we find that patterns of recruiting behavior are consistent with the Market Segment Model and that Geomarkets explain substantial variation in which high schools receive visits, even after controlling for school- and neighborhood-level covariates. The market devices that college admissions offices incorporate constitute a shared infrastructure that performs social closure – matching a socioeconomic hierarchy of communities to a socioeconomic hierarchy of colleges – prior to the evaluation of applications. We introduce the concept of infrastructural collusion: shared reliance by direct competitors on market devices that encode class hierarchy into the geography of opportunity.