What white or light grey spider has one outlined black triangle found near a huge web in topanga canyon in southern caifornia?

The spider you are describing is likely the Western Black Widow (Latrodectus hesperus), known for its distinctive appearance and the characteristic black triangle on its back. While typically black, juveniles can appear lighter in color, which might fit your description. These Spiders are often found near their webs, which are irregular and tangled, in areas like Topanga Canyon. Always exercise caution around these spiders, as their bites can be harmful.