Some 60,000 pounds of ammonium nitrate, a chemical used as both fertilizer and a component in explosives, went missing as it was shipped by rail from Wyoming to California last month, prompting four separate investigations.

A railcar loaded with 30 tons of the chemical left Cheyenne, Wyoming, on April 12. The car was found to be empty after it arrived two weeks later at a rail stop in the Mojave Desert, according to a short incident report from the explosives firm that made the shipment.

The company, Dyno Nobel, made the report May 10 to the federal National Response Center, or NRC. The report also appeared last week in an NRC database of California incidents managed by the state Office of Emergency Services last Wednesday.