I have a Mac running OSX that is one version older than yours, and had the same problem. Once I installed the CH340 drivers, then plugged in my $3 Arduino, there was a kernel panic and I had to reboot the computer. After trying every "fix" I could find on the internet, I ordered 2 of every popular USB to serial converter on ebay.
The problem is the CH340 drivers do not always work well with OSX. Some folks are lucky and they work great, and other have issues.
A permanent solution is to use a PL2303HX USB to RS232 adapter: http://www.ebay.ca/itm/For-Arduino-Module-Converter-PL2303HX-Converter-NEW-TTL-USB-To-RS232-Adapter-/142004090259?hash=item21101a7593:g:D70AAOSwSWJXRWJV. You will have to download a driver and install it first: http://www.prolific.com.tw/US/ShowProduct.aspx?p_id=229&pcid=41 (Mac OS X Universal Binary Driver v1.5.1).
To use this converter, power up the Arduino using the power jack with 7 - 9 VDC. Connect the PL2303HX ground, TX and RX to the Arduino and plug it into your computer. If a dialog box pops up just cancel it. After you click the upload button in the Arduino IDE, you will see "Binary sketch size.." in the Debug window. Press the reset button on the Arduino for 1/2 a second then release it. The sketch should upload.
The PL2303HX is VERY dependable. Plug it in, look at the Arduino > Tools > Serial Port in the IDE and there it is. Unplug the adapter then recheck the serial port and it's gone. It doesn't matter which USB port you plug it into, the port name is the same for either and should look something like this:
You can even use the PL2303HX with a "stand alone" ATMega328P-PU. Make sure to connect a 10k ohm resistor from 5 VDC to pin 1 and momentarily ground pin 1 when you see "Binary sketch size.." in the Debug window.