UPDATE: 12:20 p.m.
A witness tells the Review that crews are now working to remove the boulder.
The Trans-Canada Highway was closed at Three Valley Gap in both directions 20km west of Revelstoke for about an hour this morning.
The Review received reports that a large boulder was sitting in the middle of the highway.
A tweet from the Ministry of Transportation confirmed those reports.
Cars were backed up on Hwy. 1.
The incident comes in the same week that Revelstoke Mayor Mark McKee and Columbia River-Revelstoke MLA Doug Clovechok are meeting with Minister of Transportation and Infrastructure Claire Trevena to discuss Three Valley Gap.
In his most recent MLA report Clovechok said that he has been told a pilot project to install safety netting in Three Valley Gap will begin this summer.
The road is now open to single lane alternating traffic.
For up to date road conditions visit, DriveBC.ca.