You have a good start, but you're missing the X from clue 6. Alta Vista and 16.9 must be different.
Then you can get a lot more Xs from clues like 1, 5, and 8. Generally you would want to do those toward the end of your first pass to get as many Xs as you can around those two intersections from the left and right side of the clue.
Clue 8 will give you a lot of Xs, and it will give you the two positives from clue 5.
The left side of clue 8 can only be Escondido or Delores. In your grid, you can see that Escondido cannot be Gwen or Joan. So that means that the left side can only be Delores or something that cannot be Gwen or Joan.
So 12.5 and 1968 can never be Gwen or Joan.
Follow similar logic to place several more Xs just for clue 8. I think I got around 7 Xs for clue 8 instead of just 2. How many you get will depend on the order you work the clues.
The important one is the one that tells us that 12.5 cannot be Joan.
Since Joan cannot be 12.5, then clue 5 tells us that Joan is 1952, and Escondido is 12.5.
Then we go right back to clue 8 (now that we know Escondido is 12.5) and get another positive.
What looked pretty hopeless at first is now filling in nicely, and the rest shouldn't be too difficult.
Hope that was right.