Resources

Essential Online Resources for Hiking in California

Conditions

The National Weather Service is the best weather source generally, and the Sierra West Slope forecast is the most reliable forecast with consistent predictions for the elevation of the snow/rain line.

If snow is in the forecast or there's been a recent dump, make sure to check out the Sierra Avalanche Center for the latest avalanche hazard information.

NOAA has a great map of current snow depth.  Very good for choosing where to head out on skis or to decide if enough snow has melted away in the spring to go for a particular hike.

Check this Wildfire Map for live data from satellite based infrared sensors and CalFire for the latest on wildfires.  The air quality sensor manufacturer Purple Air also posts a map of air quality.  This can be useful in choosing hikes with the best air during fire season.

Check Caltrans to get road information if there is any wildfire activity near your destination, or there's any active snowfall.

Routes

CalTopo is my go to for planning out routes when I don't have paper maps of the area.  Make sure to check out several map layers though.  The Forest Service layers have most trails on them, but not all, and locations can be a bit approximate.  The 'Mapbuilder' layer seems to be drawing trails from open street map or some such.  That trail set is less complete, but what is there is more accurate.

All Trails and Modern Hiker are a good stop for basic info on hikes, but I find their info on dog rules are sometimes not quite correct make sure to check dog restrictions with the official websites for the park/forest/wilderness area the hikes pass through.

Summit Post is designed more for advanced climbers but you can often get useful info on walkable peaks too. 

Bob Burd is a hiking machine and meticulous documentarian of his many, many, many trips about California

Permits/Reservations

Recreation.gov is the most common place to reserve campground and wilderness backpacking permits on federal (and some state) lands.

Though most California State Parks don't allow dogs on trails, sometimes they have dog friendly campgrounds reservable online.

Sierra National Forest allows you to reserve backpacking permits, but as of 2019 you still have to mail in a paper form.  Crazy right?

California Sno Parks are handy spots to start your winter adventures from.  While the passes can be bought from local retailers, it's often better to plan ahead and order a day pass or season pass.