CHEYENNE, Wyo. (AP) — Wyoming officials have issued two notices of violation to Cloud Peak Energy Inc. following a blast at the Cordero Rojo coal mine near Gillette that registered on seismographs on the scale of a small earthquake.

No injuries were reported after the blast May 1.

State officials say the blast was so large because explosives adjacent to the blast area were also accidentally set off upon detonation, causing more than the legal limit of explosives to go off.

The state has suspended the blaster in charge of the explosion and the blaster's assistant for at least 60 days. Cloud Peak Energy must submit plans to the state outlining how it will prevent a similar explosion.

Federal mine regulators also have issued a citation, but no penalty was immediately assessed.