More than likely a canker killed the branch on your tree.  Cankers are caused by fungi, and the most common species on fruit and ornamental trees in Utah belong to the genus Cytospora.  Cytospora will attack a number of ornamental and fruit trees including peach, cherry, apricot, apple, poplar, willow, birch, and aspen.  Cytospora, and most canker-causing fungi, enters the wood through wounds as small as.  Once the pathogen has established itself in the wood, there is no way to remove it.  It will grow slowly over a period of several months, so that once you notice it, the best management option is to remove the diseased limb. 

Areas affected by cankers will have sunken and darker, discolored bark.  If you scrape the bark away, the wood underneath will be   Prune out the affected limb at least 6-inches below the canker.  Disinfect your pruners between each cut with a mixture of bleach and water.