orthoclase feldspar, one type of K-spar, with a Carlsbad twin. You can see this type of twinning in a sanidine crystal (sanidine is a related type of K-spar), and read more about K-spars at Life in Plane Light.
A view looking end on at the visible twin plane (above), and with light reflecting off the upper twin (below).
Two views with alternate twins highlighted by the sun, above and below.I recognized this feldspar as being from nearby intrusive rocks that are often porphyrytic, and which usually contain large phenocrysts of dull pink K-feldspar like this one. Having never seen any exposures of porphyry dikes or masses on our hiking hill, I wonder if this feldspar has eroded from old alluvial fan material that formed from sources now eroded or sources farther up the main canyon than our side of the hill. Either way, it makes me want to look for unmapped porphyry.