Freemont cottonwoods and why rainbows come now

The Fremont Cottonwoods along the San Diego River in Mission Gorge are now showing their best tawny foliage. You can park at the Old Mission Dam historic site or the Mission Trails Regional Park visitor center and explore the riparian area by way of riverside trails or by walking, bike riding, or skating along the bike path high above the river’s south and east banks. Large cottonwoods can also be seen along other watercourses throughout the San Diego County backcountry, including along the Sweetwater River near Cottonwood Golf Course and in Cotton- wood Valley, east of Pine Valley along Interstate 8.

Rainbow Season arrives with the first rains of late fall. Scattered showers are best for rainbow watching: sunlight refracting and reflecting through the raindrops causes two bows to appear: an intense circular arc at 42 ̊ and a bigger but weaker arc at 51 ̊ from the antisolar point (the point in the sky diametrically opposed to the sun’s position). From November through mid-February, the sun never gets higher than 42 ̊ above the horizon as seen from San Diego, so (rain and sunlight permitting) the brighter of the two arcs may appear above the horizon at any time of day. In spring and summer, rainbows are never seen in the sky around midday because the sun is too high — and the antisolar point is too low.