OpenTracks and Osmand sound good but correct my work-restricted appstore doesn't include them. Also it's an iPhone.

Maybe it would help if I pre-downloaded Google Map data covering the trail system, but that doesn't help if I can't get gpx/kml/kmz files for the trails

My Apple Maps recently told me it now does guided hiking trails, I wonder if it would work well also for mtb (to the extent that most MTB trails are also hiking trails)