Sorry for the lateness of this reply but in case you were still researching this topic I thought I'd provide a few helpful links that give you some statistical information. It looks like Santa Rosa's crime rates when averaging all the different types of crime (violent & property) are about average or "on par" with the rest of the nation. For some actual numbers: http://www.cityrating.com/citycrime.asp?city=Santa+Rosa&
In a city as large as Santa Rosa, crime is not unheard of. By and large it feels safe and walking around isn't a problem. There are different crime rates in different areas of town, and the different neighborhoods have different 'feels' about them.