It seems to start blooming in November, shortly after the first rains and it continues until May (sometimes June).
There are actually two species of Marah in our area, this and M. fabaceus which is supposed to be smaller in almost all ways. The simplistic way to distinguish them is to look at the flowers, cup-shaped flowers are this species, flat flowers are M. fabaceus. That doesn’t work very well in SB where the two seem to hybridize. You can also brave the spines and open one of the fruits. If there are 8 or more seeds it is this species, for there are 4 M. fabaceus.
Away from the coast and north of Camino Cielo most plants I’ve seen look like M. fabaceus, while further south there’s a confusing mix.
It was one of the early colonizers after the Cold and Gibraltar fires and one of the first things to bloom in the burned region.
The following is a sequence of images of one plant growing in the area of the Gibraltar Fire starting about 3 months after the burn (regrowth was slowed because of the drought. There was essentially no rain before January). The fire started 29 Oct 2015, first image 26 Jan 2016.
26 Jan, new shoots