Basalt at the foot of Frowning Ridge

I took this photo last Tuesday, the day after our nice good rain. If you weren’t outdoors last week, you missed a brief moment in the Oakland year that lasts just a few days.

1684hill

It’s the period between the first significant rain and the sprouting of the grasses.

(Before I continue, this is the last week of the scientific blog survey, to which you’re invited to respond at bit.ly/mysciblogreaders. There are prizes, plus the good feeling of helping research. More than 100 of you have already taken part.)

The first rain drenches the ground and changes the dry, gold-brown hillsides to a rare saturated dun color. Soon afterward the hills flush green, and we’re off to a new year in the Mediterranean climate cycle that governs the Bay area. Think of it like the week between Christmas and New Years, only it’s in the calendar that plants use.

This is a special hill at the southern end of Frowning Ridge, the highland that includes Grizzly Peak and its lower, gentler neighbor Chaparral Peak. Old topo maps mark it with its elevation of 1684 feet. To the right of this photo, shot from Skyline Boulevard near Radio Tower Hill, the ground plunges to the water gap and roadcut of Route 24. On the other side of 24 the ridge resumes, under the name Gudde Ridge, and rises to the peak of Round Top. The following shots from 1684 Hill are from a visit in July 2013, during the gold season of the plant calendar.

1684-view-south

Frowning Ridge is held up by the thick lava flows of the Moraga Formation. Like most of the rocks in the Oakland/Berkeley Hills, the Moraga Formation is tilted up to nearly vertical. You can reach 1684 Hill by an informal path off the Skyline Trail. The lower western slope of the ridge is underlain by Orinda Formation conglomerate, but basalt makes up its bulk.

1684-moraga-basalt

Let’s look back west toward Radio Tower Hill. Last week’s photo was taken from the little saddle at the left edge.

1684-view-west

The view north takes in the upper part of Siesta Valley. That’s Vollmer Peak in the middle, highest point in the Berkeley Hills. Grizzly Peak is just out of sight at the left, but the tip of its radio tower shows.

1684-view-north

The view east overlooks lower Siesta Valley and Mount Diablo.

1684-view-east

On a clearer day I imagine the Sierra Nevada is visible along the left horizon.

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