Since the controversial withdraw from the Paris agreement, California has taken it upon themselves to sign an agreement with China to continue green technology development.

The Logan Act of 1799 states

Any citizen of the United States, wherever he may be, who, without authority of the United States, directly or indirectly commences or carries on any correspondence or intercourse with any foreign government or any officer or agent thereof, with intent to influence the measures or conduct of any foreign government or of any officer or agent thereof, in relation to any disputes or controversies with the United States, or to defeat the measures of the United States, shall be fined under this title or imprisoned not more than three years, or both.

This agreement between California and China 1) aims to influence the conduct of China with respects to economy and green initiative, and 2) aims to defeat the measures that the US government has put forth with our withdrawl from the Paris agreement.

How is this not a cut and dry case? California is overtly driving opposition against the United States government's agenda in an act of defiance with a foreign power. China none-the-less.

Is the agreement illegal and can Governor Jerry Brown be fined/imprisoned for this?

Edit: The history of the law and where it stems from seems pretty similar.

The Logan Act was basically a response to an effort by a Philadelphia Quaker named George Logan to try to negotiate directly with the French government. This was a big scandal at the time in foreign affairs because Logan—a Democratic-Republican—was trying to thwart the policy of the Federalists, who controlled both houses of Congress and the White House.

— Steve Vladeck of the University of Texas School of Law[4]

Kevin Kearney, writing in the Emory Law Journal, described Dr. Logan's activities in France:

Upon his arrival in Paris, he met with various French officials, including Talleyrand. During these meetings, he identified himself as a private citizen, discussed matters of general interest to the French, and told his audience that anti-French sentiment was prevalent in the United States. Logan's conversation with Merlin de Douai, who occupied the highest political office in the French republic, was typical. Logan stated that he did not intend to explain the American government's position, nor to criticize that of France. Instead, he suggested ways in which France could improve relations with the United States, to the benefit of both countries. He also told Merlin that pro-British propagandists in the United States were portraying the French as corrupt and anxious for war, and were stating that any friend of French principles necessarily was an enemy of the United States. Within days of Logan's last meeting, the French took steps to relieve the tensions between the two nations; they lifted the trade embargo then in place, and released American seamen held captive in French jails. Even so, it seems that Logan's actions were not the primary cause of the Directory's actions; instead, Logan had merely provided convenient timing for the implementation of a decision that had already been made.[5]

Governor Jerry Brown flew to Beijing and signed a document in an act of defiance against the policy agenda set forth by the US Government.