Fascinating Geography!

There are so, so many things I don't understand! Here's a puzzler for me... Like many children, I learned that March 21 was "equinox" - equal hours of daylight and darkness. It was taught as a kind of universal fact. But as I check my weather app, I see that March 17, this year, was equinox in Montreal...

But much farther south-west, in Indio, California - where some of my relatives spend their winters - equinox arrived a full day earlier on March 16.

That's 5 days before March 21!

Here in Ottawa, on March 17 we were already a minute past equinox. Yet we are taught that equinox is March 21 - which is also considered the first day of spring. 

It's a puzzler to me!