A woman went scorched Earth on a lady who was walking her German Shepherd on the asphalt during SoCal's heatwave, bare paws and all ... it got toasty and it's all on video.

We're told the situation went down Wednesday outside a TJ Maxx in San Dimas, CA -- where temperatures reached over 100 degrees. Witnesses say, around 2 p.m., a blonde woman got into a heated confrontation with a younger brunette after spotting her walking her dog across the scorching hot parking lot.

We're told the blonde warned the woman her dog needed booties to protect his paws from the record-breaking heat.

Witnesses say the brunette -- who was walking her dog -- snapped back at the concerned observer ... calling her an "old, white Karen" and threatened to call police. We're told the blonde encouraged her to get cops involved ... saying walking the dog on the hot pavement was animal abuse.

The brunette fired back that her dog was fine and healthy because he had eaten his kibble that morning ... then continued toward her car with a friend and the dog.

Check out the footage, the dog appears to repeatedly lift his paws while walking on the asphalt during the heated exchange ... almost as if it was too hot to walk on.

ICYMI -- California has been experiencing a heat wave over the past month, with temperatures reaching over 100 degrees in some areas. For what it's worth, pavement can soar over 145 degrees when the air temperature is about 95°F to 100°F in direct sun, which can cause severe burns almost instantly on paws.

We're told no cops were called ... but the pavement wasn't the only thing getting heated.