The scene that unfolded recently in this desert city about 100 miles from the U.S.-Mexico border exemplifies how the immigration crisis has spilled over into communities farther north.

With a historic flow of Central American families fleeing poverty and violence, federal officials earlier this spring began releasing migrants on their own recognizance from inundated detention centers in growing numbers. About 175,000 have left custody since Dec. 21.

Nonprofit and faith-based organizations in Riverside and San Bernardino counties are among those that have stepped in to help the asylum seekers. But the mounting costs have raised doubts — among local officials and advocates alike — about how long they can keep doing so.

Many of the drop-offs have taken place in Blythe, a city of about 20,000 along the Colorado River across from Arizona. Since March, said Riverside County spokeswoman Brooke Federico, 2,600 migrants have arrived here.