Households along a three-mile area of Strath Halladale were flooded out, debris was washed across the road and a gravel driveway was riven to the core.
Highland Council roadmen worked with a digger until after midnight on Monday to clear the affected part of the single-track A897 which runs from Helmsdale to Melvich.
Two units from Highlands and Islands Fire and Rescue Service were also called out.
Crofter Alistair Fraser, Trantlebeg, described the downpour and resultant flood as “phenomenal.”
His neighbour and brother-in-law Donnie Mackay (76), who has lived in Trantlebeg all his life, said: “I’ve seen the odd flash flood with a thunderstorm but never quite of this volume.
“It wasn’t just raining, it was stotting off the deck! I’m on the east side of the Halladale and when I looked over to the west, the hill in front of us was almost a sheet of water.”
The torrential, monsoon-like rain began to pour around 3pm and did not let up in intensity for around two hours.
The area affected was a three-mile radius between Dalhavaig and Forsinain and included the small crofting communities of Trantlebeg and Trantlemore.
The two communities are on opposite sides of the Halladale River and the A897.
Mr Fraser said: “It was very localised and there would have been people in Strath Halladale who would have been completely unaware of the flooding.
“At one end of the strath a crofter was shearing his sheep and at the other end people could not venture out.”
Road culverts and drains were unable to cope with the volume of water and quickly clogged up and overflowed, Normally sedate burns on the hill above Trantlemore became swollen and burst their banks.
Seventy-five-year old Julie Haworth, a widow, could only watch in horror as the water seeped into her home, Glencraggach, Trantlemore.
She said: “I could see what was going to happen so I got things out of my garage and made barriers to try and divert the water but it still came in.
“My kitchen was flooded to above my ankles. The linoleum was floating and the carpet at the top part of the room, where my solid fuel stove is, was sodden.
“My neighbour came round to help me out and we were padding around in our bare feet mopping up.”
Mrs Haworth, who has lived at Trantlemore for 23 years, said her home had been flooded out only once before, in 2006.
She said: “When you’re on your own and this happens, clearing up just seems such a mountainous task.”
It is understood another two households, including James Henderson of 173 Trantlemore, were also flooded out but the occupants could not be contacted for comment.
Local resident, Audrey Imlach, who was working at the RSPB centre at Forsinard on Monday, returned to her home at 177 Trantlemore to find her driveway had been washed away.
She said: “I came back in the middle of it all. A friend drove me home and we had a difficult time with the amount of water on the road. The car conked out at one point.”
Ms Imlach said the culvert draining water from the roadway near her home had filled up and the water came over it “like a wave” onto her driveway.
“You could actually see the rock on my driveway moving. The water gouged out the rock and the driveway now has two enormous holes all the way down it – some of it is about two feet down. It’s quite dramatic.”
She added: “It was lucky that, although the water came very close, it didn’t come into the house.”
Ms Imlach has lived at Trantlemore for over 10 years and has experienced a flood once before, but said it was not as bad.
Highland Council community works manager Henry Flett called the incident an “act of God” and said nothing could have been done to prevent it.
He said: “I was alerted to the situation at about 7.30pm on Monday and was told that burns on the hill were overflowing their banks and water was tumbling down onto the road, bringing with it stones and debris.
“I called out three of our workers to put out signs clear the debris with a digger. The boys were there till after midnight.”
Mr Flett said the A897 did not have to be closed and was passable with care.
“The same thing happened in 2006 — heavy rain followed by a flash flood,” he said.
A spokesman for Highlands and Islands Fire and Rescue Service confirmed that two units had been sent out to Strath Halladale on Monday evening following a call from a member of the public.
He said: “We got a call at around 6.20pm and despatched two appliances from Bettyhill and Thurso. Firefighters used small gear to help unblock a drain.”
n A flash flood also caused problems on part of the north coast on Sunday.
Farr High School head teacher and Northern Times correspondent Jim Johnston said torrential rain battered the west part of Bettyhill, along with an area to the south of the A836 and between the Borgie and Naver Rivers.
The downpour lasted from 5am to 8am on Sunday.
“Smooth surfaces, such as roads, car parks and patios were carpeted in hail and within minutes all the small burns draining the area were converted to torrents,” said Mr Johnston.
“An avalanche scar from a previous episode on Naver Rock was reactivated and a burn burst its banks, leaving a permanent torrent track.
“Gravel and stones, washed on to the roads by the flash flood, was in evidence throughout the village, and on the A836 over Apigill.”
HIFRS sent the Bettyhill unit to deal with flooding reported at a holiday home, “The Captains,” at Achina.
A walker was injured on Druim Chuibhe – a ridge near Bettyhill – later on the Sunday while crossing a flooded stream.
She was carried to the ambulance by members of Assynt Mountain Rescue Team.