The Iowa Supreme Court hired a professor from the University of Northern Iowa to study sentencing to see if there was a dependence on race/ethnicity. The only dependence he found was for aggravated misdemeanors.
Two friends (now retired) looked at the prison data one for the Board of Parole and the other for Department of Corrections and I independently did the same. I figured out that the aggravated misdemeanors were because of enhanced penalties for multiple charges for driving while barred. I talked to police officers and sheriffs deputies and agreed that was the cause. They know who is barred and if they see them driving they arrest them.
Someone who lives in a rural area has to drive to work, get groceries and take their children to school activities. For them the penalty is Draconian and the legislators don't seem to care.
To understand why Iowa has such a large racial disparity you have to look at the felony pretrial population. You have to look a jail booking data and jail daily population data so you can compare the pre-sentening and post-sentencing racial disparities. It tuns out they are the same the large disparity existed before sentencing. The problem was not caused by sentencing policy.
The original question was related to sentencing policy and race and my answer is that in Iowa the racial disparity existed before sentencing. I am new so I am not familiar with rules so I don't think should take up an unasked question.
The older studies were distributed as attachments to emails. Putting reports on the web is a relatively recent practice. Sorry but the links to the studies are not available.
Criminal case processing is initiated by a report of a crime. Not all crimes are reported so you have to use victimization surveys to determine the gender age and race/ethnicity of victims. It is axiomatic that nobody wants to be a crime victim.
It turns out that young Black females are more likely to be violent crime victims than young White and Hispanic females. Note that I am comparing females to females. There are also disparities for young Black and Hispanic males but interpretation is more complex. So an age, gender and race/ethnicity disparity for victims existed at the start of criminal case processing.
Not all reports of crimes result in an arrest and the vast majority of the data on arrestees is from large jails in urban counties and many of them do not report the ethnicity so I think the best data sources are the victimization surveys.