The yellow stuff is from coyote melon, most likely or ripening prickly pears...
There was an autumn softness in the air as I day hiked with a friend along a portion of the Pacific Crest Trail near Warner Springs.“What’s that smell?” he asked as we scuffed along the well-worn path.When I realized he…
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there is a patch of melon a few miles up the drainage to the south...but given how much of it on these hills, my guess is this is most likely prickly pear.
@Gelcoater you might find this interesting: it covers some of the desert you know around here:
Have never seen that here local. Or in the hills of Yorba Linda back when there were still hills and not houses

I have seen it down in Temecula.
We were at a wedding venue owned by an old San Diego surfer dude.
He had all the cool stuff down there, those melons just pop up here and there. He has giant oaks, and those giant boulders the are are known for have the tell tale signs of native habitation. Holes worn into the rock where they grind grains.
He also had a native plant I wasn’t familiar with that also just pops up here and there.
Had white trumpet flowers and prickly balls growing.
If you know, you know.
If you don’t it’s called by several names.
My wife has an app on her phone that tells what plant something is and how well it is or isn’t growing if you point the camera at it.
Jamestown weed. Or Jimsonweed.
It’s poisonous to dogs, and if a human eats enough of it it will kill.
Apparently in small doses it will send people into a high that lasts a couple weeks, and the person will have no memory of any of their shenanigans while they were high.
Natives used to use it in ceremony.
wydaily.com