I wrote to Gen. Irvin McDowell to alert him to the possibility of rebel agitation in the state of California.
CITY POINT, VA., January 8, 1865.
Major General I. McDOWELL,
Commanding Department of the Pacific:
It is known that Doctor Gwinn, former U. S. Senator from California has gone to Mexico and taken service under the Maximillian Government. It is understood also that he has been appointed governor-general of Sonora. The doctor is a rebel of the most virulent order. His being formerly a resident of California and now getting to that State in Mexico bordering on the State of his former residence, portends no good to us. May it not be his intention to entice into Sonora the dissatisfied spirits of California, and if the opportunity occurs organize them and invade the State? I write without having discussed this question with any one, to put you on your guard against what I believe may prove a great danger. Watch this matter closely, and should you find these apprehensions well founded, prepare to meet them. You will find no difficulty in raising any number of volunteers that may be necessary in California to repel an invasion of the State. Especially will this be the case where the invasion comes from a country with which we are at peace.
In any event like the one alluded to, I would not rest satisfied with driving the invaders onto Mexican soil, but would pursue him until overtaken, and would retain possession of the territory from which the invader started until indemnity for the past and security for the future, satisfactory to the Government, was insured.
This letter, which may have to be regarded as instructions for your guidance, is written entirely without knowledge of what the President would advise in case of an invasion of our territory from that of Mexico, but with a conviction that it is right and just. The case supposed is a very different one from those that have occurred starting from Canada. In the latter case rebels have fitted out for the invasion of out for the invasion of our Northern frontier upon Canadian soil, secretly and without the knowledge of Canadian authorities. In the threatened invasion it will be the act of officials of the usurpers of the Government of Mexico, and, in my judgment, would justify direct assistance on our part to re-establish the legitimate Government over that country.
This letter is intended as private until the exigency contemplated calls for action on your part, when in will be regarded as instructions for your guidance in the absence of more recent orders.
U. S. GRANT,
The Papers of Ulysses S Grant, Vol 13, p 250-1
O.R., I, l, part 2, p 1118