BOULDER — Xcel Energy says power has been restored to about 15,000 customers in Boulder after a massive outage Monday morning.

Xcel spokesman Gabriel Romero says the cause of the outage isn't known yet.

The Boulder Daily Camera ( ) reported that traffic lights went out at several major intersections but no major accidents were reported.

Originally, Xcel said about 24,000 customers were without power but later lowered the figure.