Anyone have a guess for what type of citrus this is? It is growing in a semi-wooded area of a local park. It is a 15-20 foot juvenile seedling, has nice thorns, and has nice hardiness (it survived 4 nights in the mid 20's unprotected without damage and never received supplemental watering). The leaves have a strong citrus smell when torn, much like a lemon (though I seriously doubt this is a lemon).

Here is the leaf (which is 4 inches long):

OK, an update on the mystery citrus: the tree has fruited. Here is a photo that I took this evening. It is not a good photo at all, due to the lack of light and how high the fruit was in the tree.



I now think that this is some type of orange tree. I will somehow climb up and grab a fruit and cutting once the fruit is closer to ripening.

Sour Orange??

Sorry for the lack of terminology but the small leaf right below the large leaf is always very large in sour orange so thats off your list.
Gl on finding what it is.