Here is Sichaun style 酸菜 (suān cài)). This is made by fermenting 芥菜 (jìe cai), a type of leaf mustard, in large pots with salt and leaving it for around 30 days while being pressed by heavy weights. This is usually sold with some of the juices drawn from the mustard during processing.
Suancai
Here is 榨菜 (zhà cài), also from Sichuan (specifically from Chongqing which until 1997 was part of Sichaun, but now ruled directly from Beijing).
It uses a different type of mustard and is made by salting and pressing as above, but it is then dried and covered in a chilli paste then left a bit longer.
Zha cai
Sometimes, but not often, the chilli paste is removed before consumption.
Cleaned zha cai.
Both suancai and zha cai are often sliced and sold bagged in supermarkets. This below is zha cai from Fuling, a town in Sichuan, famous for its quality zha cai.
Both are also made in other nearby provinces.