I've built a similar mobile app for both iOS and Android (as two native applications, not sharing a code base), built on top of Parse as the back-end-as-a-service. I also teach mobile app development at the university level.

I don't think that this is a reasonable goal for a summer college student with no mobile app development experience, on either platform.

I'd suggest scoping out the project into several distinct goals:

1) List of trails on iOS 2) List of trails on Android 3) Map of trails on iOS 4) Map of trails on Android 5) Trail detail screen on iOS 6) Trail detail screen on Android 7) Plotting trail route on a map in iOS 8) Plotting trail route on a map in Android 9) Showing user's route on a map in iOS 10) Showing user's route on a map in Android

And so forth based on the requirements. Explain to the company that you are going to work from the top down, and whatever you accomplish during the summer is what you accomplish. It may just be steps 1,2,3 and 4, or it may just be 1 and 3 on iOS.

Feel free to reach out if you need help!