SAN BERNARDINO, Calif. (CNS) — Roads throughout the 660,000-acre San Bernardino National Forest in Riverside and San Bernardino counties were under a closure order Monday because of snowdrifts and other winter hazards blocking passages used to access various sites, with concerns that the next round of storms could make conditions worse.

The closure was announced and went into effect Saturday, and forest officials are tentatively planning to maintain the order until June 30, though it could be rescinded at any time should conditions improve.

“Significant winter storms in February and March have resulted in extreme snowfall on the higher elevation terrain of the forest, and continuing rains and snow melt are affecting road conditions at lower elevations,” according to a U.S. Forest Service statement. “District staff are currently working to determine to what extent damage has occurred, or if other obstacles, such as severe erosion cuts, rockslides and tree blow-downs have impacted forest roads and infrastructure. These unknown obstacles are currently hidden under the blanket of deep snow.”

Communities within the roughly one-third of the forest that lies in Riverside County, mainly along Highways 74, 243 and 371, are accessible. But some hamlets in and around the forest across the San Bernardino County line to the north remain inaccessible due to snow packs and related obstructions.

Back to back storms are forecast to wallop the inland region beginning Monday night and continuing into Wednesday.

“Snow levels will fall to 4,500 to 5,500 feet early Tuesday, then rise to 6,500 feet to 7500 feet on Tuesday morning,” according to a National Weather Service statement. “The snow level will then fall to around 4,000 feet by early Wednesday morning. ... For the mountains in San Bernardino and Riverside counties, there could be a few inches of snowfall down to 4,000 to 4,500 feet, with one to two feet from 5,000 to 6,000 feet, two to four feet from 6,000 to 7,500 feet, and locally four feet or more on the higher peaks.”

While the closure order affects more than 50 forest-maintained roads, rangers pointed out that some of the corridors leading to campgrounds, picnic areas, hiking getaways and hunting grounds “have been cleared.”

“We are seeking to make as much of the forest once again accessible to visitors as possible,” the USFS said.

The closure order does not apply to some specific permits that allow vehicular movement within the preserve, including among public safety personnel.