The two reasons I became interested in columnar cactus, and specifically Trichocereus San Pedro cactus were their aesthetically cool appearance, reaching upward of ten feet easily when mature, but also their flowers! Talk about fireworks in bloom, these pachanois as well as their cousins Bridgesiis, Peruvianus and many others really know how to attract one's eyes, but also bees, bats, birds and a bunch of other critters that love their pollen! 
Usually you can count on one, or a few flowers each season here on mature cactus, but every few years they decide to really put on a show! The first week of September of this year(2023) they were blooming in their full glory. Fortunately, the west coast, southern California specifically, most cactus really feel at home here, with their internal rhythm dialed in much as it would be in their native rangeland of South America. Countries sharing the Andean Mountains like Peru, Ecuador, and Bolivia are where they can most commonly be found. This being said, collectors from around the world, whether growing in controlledh greenhouses, basements, as well as those that seasonally move their collection of exotic plants in and outside based on weather, may also experience these awesome giant flowered heavenly gifts. Their flowers tend to last 2-3 days before wilting and either falling off if they were not pollinated by other genetically different trichs, or hanging on if pollinated, then shriveliing up and becoming a fruit pod. This process usually takes a few months until the fruit naturally ripens and self cracks open, showing their white flesh and hundreds of tiny black seeds. If you are lucky, you can collect these fruits and dry their seeds(upcoming blog), or let them naturally become food for a host of other critters attracted to their flavor, smell and nutrients. Hope you learned something here, and please never hesitate to reach out with questions, I'll always do my best to answer them quickly when I can!
Cheers
Darren at the Succulent Source. 