For 35 years, three measures — labor force participation, marriage, and birth rates — declined together, with the birth rate falling furthest to a record-low general fertility rate of 53.1 in 2025. This report argues that these trends share a common engine: the rising cost of housing relative to wages, compounded by childcare costs that now rival a mortgage. The result is a two-income trap. Housing increasingly requires two earners, yet childcare for two children — averaging about $29,100 a year and exceeding a mortgage in 45 states — consumes much of that second income. Couples respond the only way the math allows: they delay marriage and children until they can afford both a home and care, or until one salary can carry the household. Crucially, participation in the prime family-formation years (25–34) never fell — it held steady near 83–84% — which is exactly what we would expect if families need two incomes to afford a home. San Joaquin County, more affordable than coastal California, still posts above-average marriage and fertility, suggesting affordability and family formation rise and fall together.