The Mackenzies by Ana Leigh (2002, Paperback)

The last time Cole MacKenzie saw Maggie O'Shea, the daughter of his gold-hunting partner, Pop, she was a scruffy kid with dirt on her cheeks. Now the tomboy is all grown up -- and how! -- and she's Cole's sworn responsibility, since the suspicious passing of his dear old friend. But being Maggie's new legal guardian may be more than the footloose loner can handle -- especially since he's been aching of late to hold her close and tight.

How dare Cole MacKenzie think he can run her life! True, she's had a crush on him since forever, but Maggie won't be treated like a child -- especially not by a powerfully good-looking wanderer who makes her flush with wanting him. Cole says he's not ready to stay put, yet he's not going anywhere until he's satisfied Pop's death was a natural one. But will that leave Maggie enough time to prove to the man how much of a woman she's become?