EL MONTE Maria Valdez didn't consider herself an environmentalist when she pressed this city east of Los Angeles to buy land ringed with factories and railroad tracks for a new neighborhood park. The trash lot is now on its way to becoming a green oasis with a butterfly sanctuary and community garden and Valdez is undergoing a transformation of her own. Next month she will be sworn in as president of the El Monte chapter of Mujeres de la Tierra, a two-year-old environmental group that caters to Hispanic immigrants and translates as "Women of the Earth." "When you get involved...