After a 70+ mile ride at tempo effort with a few harder intervals aka hills I find that my resting HR remains 10 bpm above normal for up to 24 hrs. Does this mean I am overdoing it for optimal fitness improvement?

You might not be rested from your previous workouts. Are you getting enough rest?

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The day after a long or hard ride, my resting hr is always 10+ beats higher. I always follow it with a rest day or recovery ride day. And by the day after i'm good to go for another long or hard ride.

Doing it this way, you should get 3-4 hard rides a week, and for all but neo-pro's or pro's, this is enough to see good adaption with no threat of overtraining.

Just apply the equation, Stimulus + Recovery = Adaptation.

Are you rehydrating properly?

All good info above. HR is not dictator of performance or recovery it is only a responder. 10 beats is not a large variation as HR can fluctuate by more than that just by *thinking* about something. Check rest, recovery, fuel and hydratation are keyed in. If not, maybe you need to re-assess but if its chronic seek further advice.

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