
I'll start out with a Diablo Range Gartersnake (Thamnophis atratus zaxanthus). I've seen several over 32" but only one over 36".
This fatty was 39" long, but only had 4-1/4" of tail remaining. If it had a full tail, it should have been about 43" long:


I'm really going back in time on this Santa Cruz Gartersnake (Thamnophis atratus atratus). Caught around '76 or so, it measured 36" long and was missing 3"+ of tail:

Next up is the Coast Gartersnake (Thamnophis elegans terrestris). I've seen 7 or 8 over 36", but I've never measured one bigger than 39-1/2" long. Here are five of them which ran 38" or longer.
These 2 are 38" and 39" long:

Here's another 38.5" one which is absent the orange spotting that they normally have:

Here's one that was 39" long:

The bigger of the 2 snakes in this picture was measured at 39" back in 2013. This picture was taken in 2015, but I couldn't re-capture it to re-measure:

Next up is the California Red-sided Gartersnake (Thamnophis sirtalis infernalis). They can get over four feet long.
This one was found by my dog. She does "Track a Snek", which is gartersnake scent tracking. It measured 48.5" long:


I saw it again a year later making out with a couple small males.
This 45" one was making out with a little male. I measured it about an hour after I took this picture:

These are 43" and 46" long:

Nice looking 44" snake:

So, I would really like to see others. I know that not everyone measures stuff, but you can pretty much tell if something is over 3 foot.