The worlds oldest mountains are not in California at all.
The Barberton Greenstone Belt in South Africa is estimated at 3.4-3.6 billion years old, and generally regarded as the world’s oldest mountains.
Their age is indisputably older than anything in North America (the Appalachians / Black Hills / Porcupines / Smokies etc.) and only Western Australia lays a possible claim. Most geologists accept the Greenstone Belt as being the oldest range on Earth.
Some people attempt to dispute the Belt’s title by arguing that they are not especially tall mountains. This is a rather absurd attempt. Though they are not especially tall, they are roughly 1000 feet taller than anything in the UK (the Scottish Highlands), taller than the Adirondacks, and at over a mile in height they rise over 4000 feet from the surrounding lowlands.
The usual official definition of a mountain ranges from 1000 feet (US) to 2000 feet (UK) - and by all of these this is indisputably a substantial range. Not tall by world standards - but easily a mountain range.
Fossils indicate Bacterial life older than 3 Billion years old in the Range, Gold formed ca 3 Billion years ago, and the range showcases a more complete picture of Earth’s geological history than any other Mountain range (indeed many would argue any other region) on Earth.
A caller on the show aired today claimed the mountains in North Carolina are the oldest. She moved there from California so this is where the OP got confused.
The older a mountain gets, the shorter and more rounded it gets at the top due to erosion. The mountains in California are relatively young, therefore taller and more rugged. The mountains in the Carolina’s are probably the oldest in North America.
The oldest ROCKS have been collected in MN and Canada, which both have small mountains along the North Shore of Lake Superior. There were also mountains once at the MN/WI/IA juncture area, but I think not so old. The Appalachians were once higher than the Himalayas, indicating VERY great age; some peaks in NH/VT are nearly as high as in NC, despite more glacial wear and tear. I go with Appalachia.
Everyone here is referring to mountains as if they were stable formations that remain the same through antiquity unless acted upon by a catastrophic event. They aren’t. Mountains form where earth’s plates meet, and the plates are constantly moving. With the exception of volcanic activity and earthquakes, our lives are far too short to see the changes occur, but they do continuously. Mountains can grow as well as erode/shrink.
It’s important to recognize also that while we’re using the term to decsribe ranges above sea level, there are constantly changing ranges on the sea floor as well.
When people start talking about a billion years and more, my mind’s eye wonders what a movie would look like if it were made up of a film of one picture taken every 10,000 years. I’ll bet the amount of movement would be stunning.
‘Oldest mountains’ and ‘mountains made out of the oldest rocks’ are two very different things. Those mountains in South Africa sound like they’re made out of very old rocks, but they may or may not be the oldest mountains, it depends when they were pushed up into mountains. As TSMB said, earth’s a very dynamic place.