As promised, here is a breakdown of two often confusing topics: professor tenure and hiring practices. Here are the facts directly from the source: Dean of Faculty, Amy Marcus Newhall. In addition, further explanation comes from the Scripps Faculty Handbook. 
What happens when a faculty member retires, resigns or is displaced? 
If the position was tenure-track, then the replacement position is usually tenure-track as well. The department the position was in submits a request for replacement, which outlines why there is a need for the position. The replacement is not automatic, but close to it, with an assumption that the position will be filled. 
What is the difference between Tenured, Contract-based, and Contingent Faculty? 
Tenured faculty are those whom after demonstrating excellence in teaching, scholarship, and service for six years, are awarded with a higher level of job security. With tenure, the College has decided to commit to having a job for the faculty for the rest of his or her career. 
Contract-based faculty are hired for determined amount of time. When the contract ends, their job might end. Contract-based faculty are still eligible to receive resources from Scripps, such as research money and travel awards in order for them to continue developing their career. In addition, they are able to apply for tenure-track positions as they open. Many faculty, such as Amy Marcus Newhall herself, started their Scripps career on a contract-basis, and were then able to secure a tenure-track position. 
Contingent faculty teach classes at Scripps on a part-time basis. They may not yet have the scholarship needed to apply for a tenure-track position, and so use this position as a way to gain experience. For example, there have been language professors who start off as contingent faculty at Scripps and then move on to tenure-track positions at other colleges. Alternatively, some contingent faculty may not want the pressure of constant publishing and so voluntarily choose to not do the tenure track. 
What about Writing 50 professors? Where do they stand? 
Professors who teach Writing 50 are hired on a course-by-course basis, not a multi-year contract. They are given a stipend to teach the course. They are not eligible to apply for research funds because they are here for such a short time. The only full-time faculty in the Writing Department are Kimberly Drake and Glenn Shimshaw (Shimshaw is full-time, but not on the tenure-track). It is difficult to hire the Writing 50 instructors full-time because most students who take the course, only take it during the fall, and prefer to do so. Hiring these professors full-time would mean giving the professors courses to teach during the Spring. 
How do we decide what new faculty positions to open up?
Whenever there is the election of a new Faculty Executive Committee (FEC), there is a call out to all departments to submit materials where they list their priorities. Based on that, the committee decides what new positions to open up. In addition, they look at the current faculty-student ratio and hire in a way to keep it 10:1. For this cycle, there has been a call out for five new tenure-track positions in Feminist, Gender and Sexuality Studies (previously filled by Chris Guzaitis), Politics (unfilled), English (filled by Jacqueline Wernimont), Media Studies (unfilled) and Hispanic Studies (unfilled). The FEC is dedicated to a fair and open process when it comes to the hiring of faculty. Board members are voted on, although there is no guarantee of even representation of members across disciplines. 
In addition, for truly intercollegiate departments, the 7C Academic Dean’s committee plans the hiring of new faculty. They have made an ongoing commitment to hire two new tenure-track faculty in all three ethnic studies departments. 
The Keck Science Department works on a different, more complex level. There is currently a severe shortage of tenure-track science professors, but it is not possible to hire them due to a lack of space. Tenure-track faculty are expected to engage in research, but right now the Department is maxed out on lab and work space. Because science professors have their own lab, they are also more expensive to hire. Thus, there is planning underway for a new science building. 
Hiring of professors at Scripps, the Intercollegiate Departments and the Keck Science Department is connected because they are all paid out of the same general budget. For the Intercollegiate Departments and Keck, Scripps pays a portion of the faculty’s salary. 
How are students involved in faculty hiring and tenure procedures? 
When evaluating a faculty member for the prospect of tenure, students are asked to write letters in or against their favor. In addition, course evaluations are a critical component analyzed by the Appointment, Promotions and Tenure Committee (APT) when deciding whether or not to grant a professor tenure. In addition, winning the Student’s Choice Professor of the Year Award is something that can be put on a professor’s resume, and is seen as a huge positive.