A surge of monsoon moisture combined with warm, humid air moving in from the Pacific triggered flash flooding that hit the Grand Canyon and much of Utah over the weekend.

The National Weather Service said monsoon moisture streaming into the Southwest between an eastern ridge and a Pacific trough fueled widespread thunderstorm activity across Arizona, Utah and Colorado through Monday evening.

The flooding began Saturday in Bright Angel Canyon in Grand Canyon National Park, when storms dropped about half an inch to an inch of rain in 30 minutes, NWS meteorologist Justin Johndrow in Flagstaff told CBS News.

The flood destroyed nearly all footbridges over Bright Angel Creek and knocked out the park's water pipeline, the Transcanyon Waterline, the National Park Service said. As of Monday evening, two people were confirmed dead and one remained missing, NPS Incident Commander Dave Black said.

In Utah, the same monsoon surge caused severe flooding Saturday in Orangeville and Lynndyl, forcing evacuations and derailing 34 railroad cars,   KUTV reported.

In Orangeville, the floodwater filled local canals and river channels, with debris buildup slowing their flow, according to an ETV News report. Emergency crews responded to clear the blockage. Multiple homes and roadways in the area flooded. 

Heavy rain Monday brought the North Fork of the Virgin River, near Zion National Park, from a normal flow of about 35 cubic feet per second to a peak of 5,920 cfs, the fifth-highest reading on record, the National Weather Service in Salt Lake City reported.

As of Monday, the National Weather Service placed about two-thirds of Utah under a flood watch, with the highest risk in central and southern parts of the state, including areas near recent burn scars, slot canyons and slickrock terrain. Forecasters warned the threat would persist through at least Tuesday. 

The monsoon also renewed pressure on an already-damaged watershed in Beaver County. In July, Beaver County declared a state of emergency after flash flooding and debris flows tied to the Cottonwood Fire burn scar washed out sections of State Route 153.

In late August, before this weekend's storms, UDOT Region 4 Project Manager Devin Squire said the damage throughout the canyon remained extensive, with stretches where the road, embankment and drainage systems were completely overwhelmed. UDOT said at the time that additional storms could cause further damage. The corridor remains closed this week.