It’s mid-spring, 1961. In the kitchen of a safe house in Montgomery, Ala., Martin Luther King Jr. is tense. In the house with the 32-year-old civil rights leader are 17 students — fresh-faced college kids who, moved by King’s message of racial equality, are literally putting their lives at risk. These are the groundbreaking practitioners of nonviolent civil disobedience known as the Freedom Riders, and over the past two harrowing weeks, as they’ve traveled across the state on integrated buses, their numbers have diminished at every stop in the face of arrests, mob beatings — even fire-bombings.

Right there along with the riders, capturing the mood of the movement as it swung between exhilarated and exhausted, thrilled and terrified, was 26-year-old LIFE photographer Paul Schutzer, who covered the landmark Prayer Pilgrimage for Freedom march and rally in Washington, D.C., four years earlier and witnessed firsthand the courage and determination Dr. King inspired in his followers. (Filed along with Schutzer’s Pilgrimage photos in LIFE’s archives are notes from the magazine’s Washington bureau chief, Henry Suydam Jr., citing the energy and excitement swirling around King even then: “At the end of the ceremonies, a couple of hundred people pressed feverishly on Reverend King — seeking pictures, autographs, handshakes, or just a close look. The jam got so heavy that he had to be escorted to safety by police.”)

[MORE: “One Dream,” TIME’s multimedia tribute to MLK and the 1963 March on Washington]

Here, five decades after the Freedom Riders put their lives on the line for dignity and equal rights, and on the 50th anniversary of Senate Approval of the 1964 Civil Rights Act, LIFE.com presents photos — most of which never ran in LIFE magazine — from that heady era in U.S. history. Here are pictures charting a pivotal moment in the journey of Dr. King himself and in the nation-changing movement he led, from the monuments of Washington to the highways, rural roads, churches and bus depots of the Jim Crow American South.