I’m a young Muslim living in San Jose and I wonder if it is un-Islamic to have a friend of the opposite sex?
This depends on what one means by the word ‘friend’. Usually, this word is indicative of intimate, close and frank relations. If this is the case, then my answer would be in the negative. You see Islam has based its social structure on the institution of family. To safeguard this structure, it discourages temporary unions and male-female friendships for these often lead to excesses and tend to stimulate base emotions. Also, such relationships tend to damage the repute and honour of a lady, which are so very essential for her.
On the other hand coming into some meaningful contact with one another like for example exchanging views is a different matter. Nevertheless, developing frankness is not desirable since this affects the inner purity -- something which is the very objective of Islam. Islam wants that a person should always be mindful of inner purification in his activities and dealings. It declares that only people who have purified their souls shall enter Paradise. Therefore, every person must try as much as he can to guard his soul and to preserve the modesty within him.