Not to be the contrarian-- but before you spend a bunch of time presenting to investors -- I would present it to some people who have a likelihood of becoming customers.
You know -- the people who determine the value of your web application by choosing to use it and potentially even pay for it?
Based on my experience when you show up and start presenting to the "angels" -- they are going to ask you about what the customer's -- even beta customer's -- experience has been.
The wrong answer will be "I don't have any yet".
There are lots of places you can go, to start with go back through "this week in startups" they often mention various places around the US and occasionally around the world.
Many cities are now starting up with incubators, accelerators and the like. After the discussion between @ZulyGonzalez and myself in this answer about accelerators I would suggest you try for a new one just starting up, there have been over 80 spring up after Ycombinator kicked off and showed everyone the business model.
New accelerators will have less competition, be able to give more focus to you and be able to kick start you far more effectively, plus there is likely to be one closer to your area where your personal support base of friends and family are.
I think that before you go to present your web application in California you should try to get some feedback from angles/VCs/potential investors.
You should probably prepare a presentation or an executive summary that describes your project from all the aspects that are relevant to investors.
You can find a lot of useful information on venturehacks.com on how to find investors and how to pitch to them.
You can also find angles online. http://angel.co/ is a good example
There is no doubt that the silicon valley is the best place in the world to find investors that are interested in web technologies and, of course, web developers.
i thinks, before going to California you should first search and contact angel investors, who would show some remote interest to your idea, mean while keeping your app live out on web, for user, with optimized performance.