During a decade as a janitor at a US border station, Tom Kiefer gathered the trash left behind by thousands of undocumented immigrants, piecing together the histories of those who arrived seeking a better life. "The American Dream," at Los Angeles' Skirball Cultural Center through March, displays more than 100 photographs of these remnants, which the artist collected in secret at the Ajo, Arizona station between 2003 and 2014.