"Organic" food is food grown without use of pesticides and chemical fertilizers.
This kind of food is growing in popularity in California, even though there aren't any proven adverse health implications associated with consuming trace quantities of pesticides.
Playing it safe, of course, cannot harm. So if you can afford buying organic food, go ahead and keep on doing it. (In California, organic food is, on average, two to three times more expensive than non-organic.)
However, know what you are paying for. "Organic" does not mean "natural." For example, buying organic milk doesn't automatically guarantee that the cows that produced the milk were grass-fed.
This is an important issue, as the composition of milk from grass-fed cows is vastly different from the composition of milk from grain-fed cows. In addition, several research articles showed that the milk from grass-fed cows is healthier for the heart, significantly reduces risk of stroke, heart attack, several types of cancer, allergies, diabetes, and may help with weight loss (you can read more on this subject here).
This prompted me to conduct some more Internet research to identify milk that comes from grass-fed cows and is easily available in San Francisco shops. I found a very informative webpage, which collected information on all "organic" milks available in the US. As per this article, some of the "organic" milks do not even deserve such name!
On this website you can find a link to a rating of all organic milks available in the US: a complete list.
Based on that list I concluded that the best organic brands of milk available in San Francisco are:
(1) Organic Valley
score: 1115/1200
from grass-fed cows, not treated with hormones or antibiotics
(2) Nature's One
score: 1100/1200
from grass-fed cows, not treated with hormones or antibiotics
(3) 365 Organic from Whole Foods Brand
score: 1070/1200
from grass-fed cows, not treated with hormones or antibiotics
(4) Clover Organic
score: 1050/1200
from grass-fed cows, not treated with antibiotics, but OXYTOCIN occasionally used!!!
(5) Sunnyside (available e.g. at SaveMart, Lucky)
score: 1025/1200
from grass-fed cows, not treated with antibiotics, hormones unclear