My first attempt at a 16-mile run: crash and burn!

Well, on Sunday I attempted a challenging 16-mile run in Tilden park. I made a couple of minor miscalculations so it didn't work out so well...
I got a late start, so i didn't start my run until about 10:30. I started out by running a fairly flat 3-mile loop. I had a quick drink of water and then started on the rest of my run. This 2nd segment started with a 500ft climb in elevation over the next 2 miles. This took me up to Inspiration point. I had then planned to run out Nimitz Way for 5 miles and back to my starting point which would make for a 16-mile run. I didn't think there was water at Inspiration Point or on Nimitz Way, but I wasn't 100% sure. A mile or 2 along Nimitz way in the sun and I was ready for more water. I realized that my 13-mile loop in the sun on a warm day was going to be much too far to go without water so I changed my plans. I instead ran out Nimitz 3.5 miles and then back to my starting point with the intention of adding on the final 3 miles after drinking more water. By the time I got back to my starting point I was totally baked and decided to call it a day. 10 miles in the sun on a warm day was much too far to run without water. If I had started my run earlier it may have been fine.
So, in the future, I have to be more careful planning my long runs. I need to get a couple of 18-20 mile runs in before the Marathon and it will be important to make sure I have water available along the runs and that I'm not running out in the sun when it's hot. I grew up in San Francisco in the fog and I don't do well in the heat.
I wasn't able to push my mileage to 16 miles, but I did put in a challenging 13+ mile run that included plenty of hill running. I'll attempt another 16-mile run next weekend or the weekend after.