With funding from the NSF's Scholarships in Science, Technology, Engineering, and Mathematics (S-STEM) program, this project at California State Polytechnic University Pomona (CalPoly Pomona) will support high-achieving, low-income students with demonstrated financial need. This project will fund 146 scholarships over five years for students who are pursuing bachelor's degrees in physics and astronomy. Participating scholars will join a cohort-based mentoring and undergraduate research program spanning a diverse network of more than 50 California higher education institutions. These institutions are dedicated to the goal of increasing the number of students pursuing PhDs in physics, astronomy, and associated STEM disciplines. Led by CalPoly Pomona and the University of California Irvine in Southern California, and by San Jose State University and the University of California Santa Cruz in Northern California, more than 140 physics and astronomy faculty at the 24 California State University (CSU) and University of California (UC) campuses in the bridge network will serve as mentors to scholars supported by the project. In addition to receiving biweekly mentoring and progress monitoring by pairs of one UC and one CSU professor, these scholars will also receive full need-based scholarships during their junior and senior years, monthly professional development workshops, and supervised research opportunities via the successful NSF-funded CAMPARE program.<br/><br/>Given the size and diversity of the California secondary education system, the success of this S-STEM Track 3 project will likely significantly increase the number of PhDs nationwide earned by underrepresented minorities in the fields of physics and astronomy. All low-income students enrolled in a participating CSU campus are eligible for this California Bridge (Cal-Bridge) program, which searches for students with unusual potential, using holistic review and research-based criteria developed by successful bridge programs such as the Fisk-Vanderbilt Master's-to-PhD Bridge program. Unlike other existing bridge programs, Cal-Bridge begins with students during their formative undergraduate years, focusing on preparation rather than remediation. This multifaceted support will mitigate known barriers to graduate school entry for high-achieving, motivated students from economically disadvantaged backgrounds, and will thus greatly increase the probability they complete their undergraduate degree and gain entry to PhD programs. The project also involves multi-method social science research to understand the networks of scholars and institutions formed because of partnerships between Minority/Hispanic Serving Institutions and Research Universities, and the effect of those networks on recruitment and admissions to participating UC physics and astronomy departments. Over the five-years, social network analysis and qualitative case study methods will be used to capture patterns in Cal-Bridge Scholars' graduate school admissions and enrollment, as well as in impediments to these outcomes. These results, along with the project's growing connections with institutions beyond California, will have the potential to influence the national landscape of equitable participation by low-income students in STEM higher education.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.