Can I apply for a Schengen visa from any consulate within the US or just from my nearest one?

Strictly speaking, you should apply at the consulate in San Francisco. Article 6 of the Schengen Visa Code:

Consular territorial competence

1.   An application shall be examined and decided on by the consulate of the competent Member State in whose jurisdiction the applicant legally resides.

2.   A consulate of the competent Member State shall examine and decide on an application lodged by a third-country national legally present but not residing in its jurisdiction, if the applicant has provided justification for lodging the application at that consulate.

Justification is illustrated in the Handbook for the processing of visa applications, Part II, section 2.8, which suggests that unavailability of appointments at the competent consulate does not constitute sufficient justification.

The San Francisco consulate general describes its jurisdiction thus:

The German Consulate General in San Francisco is the official representation of the Federal Government of Germany in Northern California, Alaska, Hawaii, Idaho, Montana, Oregon, Washington, Wyoming and the American overseas territories American Samoa, Baker-, Howland-, Jarvis-, Johnston-, Midway- and Palmyra-Island.

The Los Angeles consulate general has this to say:

The Consulate General's area of jurisdiction covers the California counties of Imperial, Kern, Los Angeles, Orange, Riverside, San Bernardino, San Diego, San Luis Obispo, Santa Barbara, Ventura and the states of Arizona, Colorado, Nevada and Utah.

You can always try, however. Please come back and post an answer if you do.

In a comment, you write

For now I have just changed the appointment to go to a French consulate in SF. Probably easier to fly from Paris to Berlin in view of unavailability of appointments immediately

This strategy is unlikely to succeed. The French consulate is not competent to handle visa applications for proposed travel in which the main destination is Germany. The French consulate should therefore reject the application with instructions to apply at the German consulate.