I've read the books, never in order, for years and decided it was time to read the first book. The books are stand alone - in that the storyline does not depend on the previous books. However, there is a continuity woven throughout the series that adds interest, but it not crucial to reading in order.
The main character is a national park ranger who loves the outdoors, the solitude of nature, and the chance to get away from humans. Each novel takes place in a different national park, which while being the setting of the books, plays out as a character, as well.
It's all engrossing to read the details of the territory of the parks and hear them through the main character. Anna is likable, yet somewhat cold, endearing and tough. The author created a rich personality in Ranger Pigeon that keeps me hooked on the books.