Field population based on most recent value

[Roach]

I have a form which has a field called, "Access Type". I would like this Access Type field to be populated by a query which references the campsite number and pulls up the value for the most recent date, if present. I'm not exactly sure about the procedure as to how to set up this query.

Below is the Form design (this is based on a table of the same name).

FormTemporal
SiteNumber
ObservationDate
AccessType

Thanks for any ideas on how to approach this.