I know the first thing to add to the soil is organic matter: it gets used up fast in the hot weather.
I don't know if I would use Ironite, although Lots of people do use it. It's manufactured from mining wastes and has been found to be high in lead, which is taken up by plants. There was an article in Organic Gardening Magazine last year, I think, on the topic.
Magnesium, usually in the form of Epsom Salts, may be useful in working with clay soils.
Potassium is one of the essential nutrients for life, and is present in compost. It may be amended to the soil in the form of green sand, for one source.
Norm

I am in the North Valley and mostly have clay soil but have a few sandy areas. Try using composted cotton burs, work it into the the soil before planting. Organic matter will help you more than trace elements (ironite)

Good Luck!
Jeff

Thanks, all, especially about Ironite! Man, I don't need that kind of toxin in my soil! I do add organic matter (compost, alfalfa feed) and will do some epsom salts. I do lots of container gardening, but some things in the ground would be nice, too.