"The common name miner's lettuce refers to its use by California Gold Rush miners who ate it to get their vitamin C to prevent scurvy.
It can be eaten as a leaf vegetable. Most commonly it is eaten raw in salads, but it is not quite as delicate as other lettuce.
Sometimes it is boiled like spinach, which it resembles in taste. Miner's lettuce can sometimes accumulate toxic amounts of soluble oxalates.[1]"

(This is from Wikipedia)

It also says that it is a "fleshy annual plant native to the western mountain and coastal regions of North America from southernmost Alaska
and central British Columbia south to Central America, but most common in California in the Sacramento and northern San Joaquin valleys."

It is plentiful near us.