I recently purchased a healthy Dragon fruit plant from Southern California, but when I brought it back to the Bay Area, the top off the plant started turning yellow. It's been fairly warm and I water it twice in a week. I finally cut that part off.

What could this indicate? And how can I help save this plant?

Well, it's (more or less) a cactus so you might be over-watering it. I'd cut back to once a week. They can take lots of water sproradically - here we get heavy rain off and on all summer - as long as it has excellent drainage. Does the water flow through the pot readily? You'll want to let it dry out well between watering it. They love heat and sun so your weather is to its liking.

These things are slow-growing so you can't expect similar growth to a regular leafy plant. Leave it be for a while and see what happens. I fertilize mine by spraying soluble fertilizer on the stems, not pouring it in the pot. They both absorb and store water and nutrients in the stems.

But to be honest, the last picture looks fine to me. If the remaining stems start to feel soft, that's when you can start to worry.

Thank you! I will try that. I greatly appreciate your feedback