The "we should have turned around at the first missing marker" line is easy to say after the fact, but that would have been the wrong call. Losing a few posts on a loop trail does not mean the trail is gone, it just means you pay more attention to the cairns, and cairns are honestly more reliable out there anyway since storms knock down wood but rocks stay put. Park crews can only do so much after a big weather event, they have hundreds of miles of trail and a small staff, so waiting on them to fix every post before you hike is not realistic. Your buddy wants a rule that makes him feel safe, but turning back every time a marker is missing means you never finish anything. If you had a map and knew how to read it, that dry creek split would not have cost you two hours.

Wait, did you check your owner's manual on the jack points first? The reason most folks leave it flat is that on a lot of cars the drain plug sits at the back of the pan, so raising the front actually tips the oil away from the hole and you leave more old oil in there than you'd think. Your Civic might drain fine either way, but on some cars you'd barely get a trickle. The other thing is if you jack up just the front, the car isn't level, so you can't trust the dipstick to tell you if you got the right amount back in. Next time try ramps instead of a jack and stands if you just need a few inches, way faster and safer.