Orange and black bug
The insect is the larva (youngster) of a lady beetle. See this info about one of the many lady beetles here in the northwest: "Sevenspotted lady beetle" http://ipm.ucanr.edu/PMG/NE/coccinella_septempunctata.html.
These larvae were probably feeding on the aphids on the tossed plum trimmings. See "Aphids" at http://ipm.ucanr.edu/PMG/PESTNOTES/pn7404.html.