If you grew up on the left coast, particularly California, baja hoodies emerged during the 70s as surfers would take trips to Baja California to chase waves and come back with a new fashion accoutrement. For much of the rest of the country, including myself in the Boston area, our introduction to baja hoodies / jerga hoodies didn't happen until 1982 or later via Jeff Spicoli and the movie Fast Times at Ridgemont High. Even the newspaper at my alma mater traces the history back to the 70s (yes, a shameless plug). That being said, Vice rolls it back 4 decades earlier to the 1930s, but not much detail so will assume it was a gradual adoption by the California and west coast surfing community.
"In the 1930s, when the sport was still a fledgling pastime on the West Coast, American surfers looking for new breaks and tourist-free beaches headed south, to Baja California, Mexico. They saw the pullover jackets worn by locals—striped like traditional Mexican serape blankets—and adopted the style (sudadera de jerga in Spanish) for themselves."
Another article details the origins back to the 1300s in South America, Chile, and an indigenous group called the Mapuche. Unfortunately, this was the only reference I could find for this, and more challenging is that if accurate, how did these evolve over the last 700+ years? Seems like this could make an interesting thesis for someone studying textiles in school. All I can attest to is baja hoodies are super warm and hold up extremely well when there's a light rain so living in PDX and spending lots of time on the Oregon coast, I have taken to wearing my baja hoodie almost year round and just about everyday from Oct - Mar.
With the growing legalization of marijuana, surfing shedding it's stoner image and casual dress becoming much more common in the last couple of decades, baja hoodies / jerga hoodies have quietly joined the mainstream.