SAN LUIS, Colo. — Each morning as the sun curves over Main Street in this isolated desert town, Felix Romero takes the worn wooden steps from his upstairs apartment to his downstairs grocery.

He flips open the lock on a scratched blue door, turns on the lights and begins to sweep, just as his family has done since 1857.

But R&R Market — the oldest business in Colorado, built by descendants of Spanish conquistadors in the oldest town in the state — is in danger, at the edge of closing just as rural groceries from Maine to California face similar threats to their existence.

“If that little store closes, it’s going to be catastrophic,” said Bob Rael, director of the economic development council in Costilla County, where San Luis is the seat. “Reality is going to set in. Who let this happen?”